View source for Daylight saving time

{{Short description|Seasonal change of clock settings}}
{{Redirect-multi|3|DST|Daylight savings|Summer time|the film|Daylight Savings (film){{!}}''Daylight Savings'' (film)|the season|Summer|other uses|DST (disambiguation)|and|Summertime (disambiguation){{!}}Summertime}}
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{{Use dmy dates|date=March 2024}}
{{Use American English|date=March 2025}}

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[[File:DST Countries Map.png|upright=1.5|thumb
|alt=World map. Europe, most of North America, parts of southern South America, and southeastern Australia, and a few other places use DST. Most of equatorial Africa and a few other places near the equator have never used DST as the seasons are not marked by drastic changes in light. The rest of the landmass is marked as formerly using DST.|Daylight saving time regions:

{{legend|#1a80e6|[[Northern Hemisphere]] summer}}
{{legend|#ee690a|[[Southern Hemisphere]] summer}}
{{legend|#c6c6c6|Formerly used daylight saving}}
{{legend|#7f7f7f|Never used daylight saving}}]]
'''Daylight saving time''' ('''DST'''), also referred to as '''daylight savings time''',{{void|Don't remove "savings time". This has been discussed on the talk page, and reliable sources were found for this usage.}} '''daylight time''' ([[Daylight saving time in the United States|United States]] and [[Daylight saving time in Canada|Canada]]), or '''summer time''' ([[British Summer Time|United Kingdom]], [[Summer time in Europe|European Union]], and others), is the practice of advancing clocks to make better use of the longer daylight available during [[summer]] so that darkness falls at a later clock time. The standard implementation of DST is to set clocks forward by one hour in [[spring (season)|spring]] or late winter, and to set clocks back by one hour to [[standard time]] in the [[autumn]] (or ''fall'' in North American English, hence the [[mnemonic]]: "spring forward and fall back").

In several countries, the number of weeks when DST is observed is much longer than the number devoted to standard time.
 
== Overview ==
As of 2023, around 34 percent of the world's countries use DST, primarily in Europe and North America.<ref>{{cite web | last=Haines | first=Julia | title=Which Countries Observe Daylight Saving Time? | website=US News & World Report | date=November 6, 2023 | url=https://www.usnews.com/news/best-countries/articles/2023-11-06/which-countries-observe-daylight-saving-time | access-date=November 4, 2024 | archive-date=20 September 2024 | archive-url=https://web.archive.org/web/20240920030932/https://www.usnews.com/news/best-countries/articles/2023-11-06/which-countries-observe-daylight-saving-time | url-status=live }}</ref> Some countries observe it only in some regions. Canada largely observes DST, with the exceptions of [[Yukon Time Zone|Yukon]], most of [[Time in Saskatchewan|Saskatchewan]], and parts of [[Nunavut]], [[British Columbia]] and [[Quebec]]. It is observed by four Australian states and one territory. [[Daylight saving time in the United States|In the United States]], it is observed by all states except Hawaii, [[Time_in_Arizona|Arizona]] (within the latter, however, the [[Navajo Nation]] does observe it), and the [[U.S. Territories]].<ref>{{cite web|url=https://www.timeanddate.com/time/us/arizona-no-dst.html |title=No DST in Most of Arizona }}</ref>

Historically, several{{example needed|plural=yes|reason=More than one example needed|date=November 2025}} ancient societies adopted seasonal changes to their timekeeping to make better use of daylight; [[Roman timekeeping]] even included changes to [[water clock]]s to accommodate this. However, these were changes to the time divisions of the day rather than setting the whole clock forward.<ref name=carcopino>{{cite book |title =Daily Life in Ancient Rome: The People and the City at the Height of the Empire |author =Jérôme Carcopino |publisher =Yale University Press |chapter =The days and hours of the Roman calendar |isbn =978-0-300-00031-3 |year =1968 |author-link =Jérôme Carcopino |url =https://archive.org/details/dailylifeinancie00carc_0 }}</ref> In a satirical letter to the editor of the ''[[Journal de Paris]]'' in 1784, [[Benjamin Franklin]] suggested that if [[Parisians]] could only wake up earlier in the summer they would economize on candle and oil usage, but he did not propose changing the clocks.<ref>{{Cite web |date=7 July 2017 |title=Did Ben Franklin Invent Daylight Saving Time? |url=https://www.fi.edu/benjamin-franklin/daylight-savings-time |url-status=live |archive-url=https://web.archive.org/web/20210601024205/https://www.fi.edu/benjamin-franklin/daylight-savings-time |archive-date=1 June 2021 |access-date=5 August 2021 |website=The Franklin Institute |language=en}}</ref><ref>{{Cite web |title=Full text – Benjamin Franklin – The Journal of Paris, 1784 |url=http://www.webexhibits.org/daylightsaving/franklin3.html |url-status=live |archive-url=https://web.archive.org/web/20171115130303/http://www.webexhibits.org/daylightsaving/franklin3.html |archive-date=15 November 2017 |access-date=5 August 2021 |website=www.webexhibits.org}}</ref> In 1895, [[New Zealand]] entomologist and astronomer [[George Hudson (entomologist)|George Hudson]] made the first realistic proposal to change clocks by two hours every spring to the [[Wellington Philosophical Society]], but this was not implemented until 1928 and in another form.<ref name="DNZB-Hudson" /> In 1907, [[William Willett]] proposed the adoption of [[British Summer Time]] as a way to save energy; although seriously considered by Parliament, it was not implemented until 1916.<ref name="Ogle" />

The first implementation of DST was by [[Port Arthur, Ontario|Port Arthur]] (today merged into [[Thunder Bay]]), in Ontario, Canada, in 1908, but only locally, not nationally.<ref name="Northern Ontario Travel">{{Cite news |date=8 March 2018 |title=Time to change your clocks – but why? |url=https://www.northernontario.travel/thunder-bay/the-thunder-bay-connection-to-daylight-savings-time |url-status=live |archive-url=https://web.archive.org/web/20181010011523/https://www.northernontario.travel/thunder-bay/the-thunder-bay-connection-to-daylight-savings-time |archive-date=10 October 2018 |access-date=9 October 2018 |work=Northern Ontario Travel |language=en}}</ref><ref name="Daylight Saving Time">{{citation |title=Daylight Saving Time |url=https://www.timeanddate.com/time/dst/ |access-date=8 October 2018 |archive-url=https://web.archive.org/web/20181009153519/https://www.timeanddate.com/time/dst/ |archive-date=9 October 2018 |url-status=live}}</ref> The first nation-wide implementations were by the [[German Empire|German]] and [[Austria-Hungary|Austro-Hungarian]] Empires, both starting on 30 April 1916. Since then, [[daylight saving time by country|many countries]] have adopted DST at various times, particularly since the [[1970s energy crisis]].<ref>{{Cite web |last=Timezig |title=Complete History of Daylight Saving Time {{!}} DST Timeline |url=https://timezig.com/dst-history |access-date=2025-10-01 |website=timezig.com |language=en |quote=1973 Energy Crisis Response Oil crisis led to emergency DST extensions in many countries to save energy.}}</ref>

==Rationale==
[[File:Clepsydra-Diagram-Fancy.jpeg|thumb|upright|alt=A water clock. A small human figurine holds a pointer to a cylinder marked by the hours. The cylinder is connected by gears to a water wheel driven by water that also floats, a part that supports the figurine.|
An ancient [[water clock]] that lets hour lengths vary with season]]

[[Industrial society|Industrialized societies]] usually follow a clock-based schedule for daily activities that do not change throughout the course of the year. The time of day that individuals begin and end work or school, and the coordination of [[Public transport|mass transit]], for example, usually remain constant year-round. In contrast, an [[agrarian society]]'s daily routines for work and personal conduct are more likely governed by the length of daylight hours<ref name="Minnesota">{{cite news |title= Daylight savings time |url= http://www.house.leg.state.mn.us/hinfo/swkly/1995-96/select/time.txt |work= Session Weekly |publisher= Minnesota House Public Information Office |year= 1991 |access-date= 7 August 2013 |archive-date= 16 June 2016 |archive-url= https://web.archive.org/web/20160616230715/http://www.house.leg.state.mn.us/hinfo/swkly/1995-96/select/time.txt |url-status= live }}</ref><ref name="RoSPA">{{cite web |title= Single/Double Summer Time policy paper |date= October 2006 |publisher= Royal Society for the Prevention of Accidents |archive-url= https://web.archive.org/web/20120913125519/http://www.rospa.com/RoadSafety/info/summertime_paper2006v2.pdf|archive-date=13 September 2012 |url= http://www.rospa.com/roadsafety/info/summertime_paper2006v2.pdf}}</ref> and by [[solar time]], which change [[season]]ally because of the Earth's [[axial tilt]]. North and south of the [[tropics]], daylight lasts longer in that hemisphere's summer and is shorter in that hemisphere's [[winter]], with the effect becoming greater the farther one moves away from the [[equator]]. DST is of little use for locations near the Equator, because these regions see only a small variation in daylight over the course of the year.

After synchronously resetting the clocks in a region to one hour ahead of standard time in spring in anticipation of longer daylight hours, individuals following a clock-based schedule will be awakened an hour earlier in the solar day than they would have been otherwise. They will begin and complete daily work routines an hour earlier; in most cases, they will have an extra hour of daylight available to them after their workday activities.<ref name="Hudson_1895_p734">{{cite journal |author-first= G. V. |author-last=Hudson |title= On seasonal time-adjustment in countries south of lat. 30° |journal= Transactions and Proceedings of the New Zealand Institute |year= 1895 |volume= 28 |page= 734 |url= http://rsnz.natlib.govt.nz/volume/rsnz_28/rsnz_28_00_006110.html |access-date= 3 April 2009 |archive-date= 30 March 2019 |archive-url= https://web.archive.org/web/20190330083629/http://rsnz.natlib.govt.nz/volume/rsnz_28/rsnz_28_00_006110.html |url-status= live }}</ref>{{sfnp|''Seize the Daylight''|2005|pp=115–118}}

The clock shift is partly motivated by practicality. At the summer solstice, in American temperate latitudes, for example, the sun rises around 04:30 standard time and sets around 19:30. Since most people are asleep at 04:30, it is seen as practical to treat 04:30 as if it were 05:30, thereby allowing people to wake closer to the sunrise and be active in the evening light, as the sun under DST sets an hour later (20:30).

Proponents of daylight saving time argue that most people prefer more daylight hours after the typical "[[Working time#Workweek structure|nine to five]]" workday.<ref>{{cite web|url= http://www.snopes.com/science/daylight.asp|last= Mikkelson|first= David|title= Daylight Saving Time|website= Snopes|date= 13 March 2016|access-date= 17 October 2016}}</ref><ref name="Willett100">{{cite web |title= 100 years of British Summer Time |url= http://www.nmm.ac.uk/explore/astronomy-and-time/time-facts/british-summer-time/ |year= 2008 |publisher= National Maritime Museum |archive-url= https://web.archive.org/web/20141228021630/http://www.nmm.ac.uk/explore/astronomy-and-time/time-facts/british-summer-time |archive-date= 28 December 2014}}</ref> Supporters have also argued that DST decreases [[energy consumption]] by reducing the need for lighting and heating, but the actual effect on overall energy use is heavily disputed.<ref name="Yuhas 2024 x931">{{cite web | last=Yuhas | first=Alan | title=When Is Daylight Saving Time? | website=The New York Times | date=March 6, 2024 | url=https://www.nytimes.com/article/daylight-saving-time-questions.html | quote="One of the oldest arguments for daylight saving time is that it can save energy costs. There have been many conflicting studies about whether actually it does." | access-date=March 20, 2024 | archive-date=20 March 2024 | archive-url=https://web.archive.org/web/20240320192003/https://www.nytimes.com/article/daylight-saving-time-questions.html | url-status=live }}</ref><ref name="Visé 2023 g495">{{cite web | last=Visé | first=Daniel de | title=Is Daylight saving time a scam? Time, money may not be saved | website=USA TODAY | date=November 3, 2023 | url=https://www.usatoday.com/story/money/2023/11/03/daylight-saving-time-money-time-not-saved/71419089007/ |quote=" ... researchers announced that the nation had reduced its energy consumption by an annual rate of 0.03%. The meager savings came in reduced electricity consumption in the evenings during the extra days of daylight time. Other research, however, has suggested the reverse: The semiannual time shift exacts a cost, and daylight time nets little or no savings." | access-date=March 20, 2024}}</ref> For evaluation, it is required to go beyond considering only energy demand for lighting and also consider the energy used for heating or cooling buildings.<ref>{{citation|author-first1=Eggimann |author-last1=Sven|author-first2= Robin |author-last2=Mutschler|author-first3=Kristina |author-last3=Orehounig|author-first4= Massimo |author-last4=Fiorentini |date=2023 |doi=10.1088/1748-9326/acb0e3 |issn=1748-9326 |issue=2 |periodical=Environmental Research Letters |title=Climate change shifts the trade-off between lower cooling and higher heating demand from daylight saving time in office buildings |volume=18|page=024001 |bibcode=2023ERL....18b4001E |doi-access=free }}<!-- auto-translated from German by Module:CS1 translator --></ref>

===Variation within a time zone===
The effect of daylight saving time also varies according to how far east or west the location is within its [[time zone]], with locations farther east inside the time zone benefiting more from DST than locations farther west in the same time zone.<ref>{{Cite news|url=https://www.washingtonpost.com/news/wonk/wp/2016/03/11/why-daylight-saving-time-isnt-as-terrible-as-people-think/|title=Why daylight saving time isn't as terrible as people think|last=Swanson|first=Anna|date=11 March 2016|newspaper=The Washington Post|access-date=27 March 2018|archive-date=11 March 2018|archive-url=https://web.archive.org/web/20180311200341/https://www.washingtonpost.com/news/wonk/wp/2016/03/11/why-daylight-saving-time-isnt-as-terrible-as-people-think/|url-status=live}}</ref> 

==History==
Ancient civilizations adjusted daily schedules to the sun more flexibly than DST does, often dividing daylight into 12 hours regardless of daytime, so that each daylight hour became progressively longer during spring and shorter during autumn.<ref>{{cite journal |title= Daylight saving in ancient Rome |author= Berthold |journal= The Classical Journal |volume= 13 |issue= 6 |pages= 450–451 |year= 1918 }}</ref> For example, the [[Roman timekeeping|Romans kept time]] with [[water clock]]s that had different scales for different months of the year; at Rome's latitude, the third hour from sunrise ([[terce|''hora tertia'']]) started at 09:02 [[solar time]] and lasted 44 minutes at the winter [[solstice]], but at the summer solstice it started at 06:58 and lasted 75 minutes.<ref name=carcopino /> From the 14th century onward, equal-length civil hours supplanted unequal ones, so [[civil time]] no longer varied by season. Unequal hours are still used in a few traditional settings, such as monasteries of [[Mount Athos]]<ref>{{cite journal |journal =The Atlantic |year =2003 |volume =292 |issue =5 |pages =138–141 |title =The holy mountain |author =Robert Kaplan |author-link =Robert D. Kaplan}}</ref> and in Jewish ceremonies.<ref>{{cite book |author =Hertzel Hillel Yitzhak |year =2006 |title =Tzel HeHarim: Tzitzit |chapter =When to recite the blessing |pages =53–58 |isbn =978-1-58330-292-7 |publisher =Feldheim |location =Nanuet, NY }}</ref>

[[Benjamin Franklin]] published the proverb "early to bed and early to rise makes a man healthy, wealthy, and wise",<ref>{{cite book |url = https://books.google.com/books?id=fgaUQc8NbTYC&pg=PA70 |title = The Facts on File dictionary of proverbs |page = 70 |first = Martin H. |last = Manser |publisher = [[Infobase Publishing]] |year = 2007 |access-date = 26 October 2011 |isbn = 978-0-8160-6673-5 |archive-date = 4 September 2015 |archive-url = https://web.archive.org/web/20150904045548/https://books.google.com/books?id=fgaUQc8NbTYC&pg=PA70 |url-status = live }}</ref><ref>{{cite book |url =https://books.google.com/books?id=EYiyAAAAIAAJ&pg=PA477 |title =Memoirs of Benjamin Franklin |author1 =Benjamin Franklin |author2 =William Temple Franklin |author3 =William Duane |publisher =McCarty & Davis |year =1834 |page =477 |access-date =20 October 2016 |archive-date =1 February 2017 |archive-url =https://web.archive.org/web/20170201213811/https://books.google.com/books?id=EYiyAAAAIAAJ&pg=PA477 |url-status =live }}</ref> and published a letter in the ''[[Journal de Paris]]'' when he was an American [[Envoy (title)|envoy]] to France (1776–1785) suggesting that Parisians economize on candles by rising earlier to use morning sunlight.<ref>{{cite journal |author =Seymour Stanton Block |title =Benjamin Franklin: America's inventor |journal =American History |year =2006 |url =http://www.historynet.com/benjamin-franklin-americas-inventor.htm |access-date =9 March 2009 |archive-date =29 March 2019 |archive-url =https://web.archive.org/web/20190329120837/https://www.historynet.com/benjamin-franklin-americas-inventor.htm |url-status =live }}</ref> This 1784 satire proposed taxing window shutters, rationing candles, and waking the public by ringing church bells and firing cannons at sunrise.<ref name=Franklin>{{cite journal |author =Benjamin Franklin, writing anonymously |title =Aux auteurs du Journal |journal =Journal de Paris |date =26 April 1784 |issue =117 |pages =511–513 |language =fr }} Its first publication was in the journal's "Économie" section in a French translation. The [http://www.webexhibits.org/daylightsaving/franklin3.html revised English version] {{Webarchive|url=https://web.archive.org/web/20171115130303/http://www.webexhibits.org/daylightsaving/franklin3.html |date=15 November 2017 }} [cited 13 February 2009] is commonly called "An Economical Project", a title that is not Franklin's; see {{cite journal |author =A.O. Aldridge |title =Franklin's essay on daylight saving |journal =American Literature |volume =28 |issue =1 |pages =23–29 |year =1956 |doi =10.2307/2922719|jstor =2922719 |issn = 0002-9831 }}</ref> Despite common misconception, Franklin did not actually propose DST; 18th-century Europe did not even keep precise schedules. However, this changed as rail transport and communication networks required a standardization of clocks unknown in Franklin's day.<ref>{{cite journal |author =Eviatar Zerubavel |title =The standardization of time: a sociohistorical perspective |journal =The American Journal of Sociology |volume =88 |issue =1 |year =1982 |pages =1–23 |doi =10.1086/227631 |s2cid =144994119 |author-link =Eviatar Zerubavel }}</ref>

In 1810, the Spanish National Assembly [[Cortes of Cádiz]] issued a regulation that moved certain meeting times forward by one hour from 1 May to 30 September in recognition of seasonal changes, but it did not change the clocks. It also acknowledged that private businesses were in the practice of changing their opening hours to suit daylight conditions, but they did so of their volition.<ref>{{cite book |url=http://www.congreso.es/docu/blog/reglamento_cortes_1810.pdf |series=[[Congreso de los Diputados]] |place= Cadiz |title=Reglamento para el gobierno interior de las Cortes |first=Manuel |last=Luxan |year=1810 |archive-date=5 September 2018 |archive-url=https://web.archive.org/web/20180905065227/http://www.congreso.es/docu/blog/reglamento_cortes_1810.pdf |url-status=live }}</ref><ref>{{cite news |url=http://www.elmundo.es/opinion/2018/09/03/5b8bd39046163f9c628b462e.html |newspaper=[[El Mundo (Spain)|El Mundo]] |last=Martín Olalla |first=José María |date=3 September 2018 |access-date=4 September 2018 |title=La gestión de la estacionalidad |language=es |publisher=[[Unidad Editorial]] |archive-date=4 September 2018 |archive-url=https://web.archive.org/web/20180904101703/http://www.elmundo.es/opinion/2018/09/03/5b8bd39046163f9c628b462e.html |url-status=live }}</ref>

[[File:George-Vernon-Hudson-RSNZ.jpeg|thumb|upright|left|alt= Fuzzy head-and-shoulders photo of a 40-year-old man with a mustache.|[[George Hudson (entomologist)|George Hudson]] was the first to propose modern DST, in 1895.]]

New Zealand entomologist [[George Hudson (entomologist)|George Hudson]] first proposed modern DST. His shift-work job gave him spare time to collect insects and led him to value after-hours daylight.<ref name="DNZB-Hudson">{{DNZB|last= Gibbs|first= George|id= 3H42|title= Hudson, George Vernon|access-date= 22 March 2015}}</ref> In 1895, he presented a paper to the [[Royal Society of New Zealand#Regional Constituent Organisations|Wellington Philosophical Society]] proposing a two-hour daylight-saving shift,<ref name="Hudson_1895_p734"/> and considerable interest was expressed in [[Christchurch]]; he followed up with an 1898 paper.<ref>{{cite journal |author =G. V. Hudson |title =On seasonal time |journal =Transactions and Proceedings of the New Zealand Institute |year =1898 |volume =31 |pages =577–588 |url =http://rsnz.natlib.govt.nz/volume/rsnz_31/rsnz_31_00_008570.html |access-date =3 April 2009 |archive-date =23 May 2010 |archive-url =https://web.archive.org/web/20100523181524/http://rsnz.natlib.govt.nz/volume/rsnz_31/rsnz_31_00_008570.html |url-status =live }}</ref> Many publications credit the DST proposal to prominent English builder and outdoorsman [[William Willett]],<ref>{{cite journal |title =New Zealand time |journal =New Zealand Geographer |date =1 October 1947 |volume =3 |issue =2 |page =198 |doi =10.1111/j.1745-7939.1947.tb01466.x |last1 =Lee |first1 =L. P. |author-link=Laurence Patrick Lee |bibcode =1947NZGeo...3..197L }}</ref> who independently conceived DST in 1907 during a pre-breakfast ride when he observed how many Londoners slept through a large part of a summer day.<ref name="Willett100"/> Willett also was an avid golfer who disliked cutting short his round at dusk.{{sfnp|''Seize the Daylight''|2005|p=3}} His solution was to advance the clock during the summer, and he published the proposal two years later.<ref name=Willett>{{cite book |author =William Willett |title =The waste of daylight |year =1907 |edition =1st |url =http://www.webexhibits.org/daylightsaving/willett.html |author-link =William Willett |via =Daylight Saving Time |access-date =9 March 2009 |archive-date =30 March 2019 |archive-url =https://web.archive.org/web/20190330085246/http://www.webexhibits.org/daylightsaving/willett.html |url-status =live }}</ref> Liberal Party member of parliament [[Robert Pearce (British politician)|Robert Pearce]] took up the proposal, introducing the first Daylight Saving Bill to the British House of Commons on 12 February 1908.<ref>{{cite hansard | url = https://api.parliament.uk/historic-hansard/commons/1908/feb/12/daylight-saving-bill#S4V0184P0_19080212_HOC_254 | title = Daylight Saving Bill | house = House of Commons | date = 12 February 1908 | column_start = 155 | column_end = 156 }} {{Webarchive|url=https://web.archive.org/web/20231010163705/https://api.parliament.uk/historic-hansard/commons/1908/feb/12/daylight-saving-bill#S4V0184P0_19080212_HOC_254 |date=10 October 2023 }}</ref> A select committee was set up to examine the issue, but Pearce's bill did not become law and several other bills failed in the following years.<ref name=Ogle>{{Cite book|last=Ogle|first=Vanessa|url=https://books.google.com/books?id=R5_XCgAAQBAJ&pg=PA51|title=The Global Transformation of Time: 1870–1950|date=2015|publisher=Harvard University Press|isbn=978-0-674-28614-6|page=51|language=en|access-date=4 December 2020|archive-date=22 March 2021|archive-url=https://web.archive.org/web/20210322224631/https://books.google.com/books?id=R5_XCgAAQBAJ&pg=PA51|url-status=live}}</ref> Willett lobbied for the proposal in the UK until his death in 1915.

[[File:Saving Daylight - Save 1,000,000 tons of coal NMAH-AC0433-0000103.jpg|thumb|upright|right|DST was first implemented in the United States to conserve energy during World War I (poster by [[United Cigar Stores]]).]]
[[Port Arthur, Ontario]], Canada, was the first city in the world to enact DST, on 1 July 1908.<ref name="Northern Ontario Travel"/><ref name="Daylight Saving Time"/> This was followed by [[Orillia]], Ontario, introduced by William Sword Frost while mayor from 1911 to 1912.<ref>{{cite web |url =http://www.orilliapacket.com/2009/07/16/faded-memories-for-sale |last =Moro|first =Teviah |title =Faded Memories for Sale |newspaper =Orillia Packet and Times|date =16 July 2009 |location =Orillia, Ontario |access-date =20 October 2016 |url-status=dead |archive-url =https://web.archive.org/web/20160826093846/http://www.orilliapacket.com/2009/07/16/faded-memories-for-sale |archive-date =26 August 2016}}</ref> The first states to adopt DST ({{langx|de|Sommerzeit}}) nationally were those of the [[German Empire]] and its [[World War I]] ally [[Austria-Hungary]] commencing on 30 April 1916, as a way to conserve coal during wartime. Britain, most of its [[Allies of World War I|allies]], and many European neutrals soon followed. Russia and a few other countries waited until the next year, and the United States adopted daylight saving in 1918. Most jurisdictions abandoned DST in the years after the war ended in 1918, with exceptions including Canada, the United Kingdom, France, Ireland, and the United States.<ref>{{cite book |url=http://biblio-archive.unog.ch/Dateien/CouncilMSD/C-667-M-267-1923-VIII_EN.pdf |last=League of Nations |title=Regulation of summer time |date=20 October 1923 |location=Geneva |pages=5, 22–24 |access-date=4 September 2020 |archive-date=24 October 2020 |archive-url=https://web.archive.org/web/20201024144826/https://biblio-archive.unog.ch/Dateien/CouncilMSD/C-667-M-267-1923-VIII_EN.pdf |url-status=dead}}</ref> It became common during [[World War II]] (some countries adopted double summer time), and was standardized in the US by federal law in 1966, and widely adopted in Europe from the 1970s as a result of the [[1970s energy crisis]]. Since then, the world has seen many enactments, adjustments, and repeals.{{sfnp|Seize the Daylight|2005|pp=51–89}}

It is a common [[myth]] in the United States that DST was first implemented for the benefit of farmers.<ref name="Feltman-2015">{{Cite news |last=Feltman |first=Rachel |date=6 March 2015 |title=Perspective {{!}} Five myths about daylight saving time |language=en-US |newspaper=Washington Post |url=https://www.washingtonpost.com/outlook/2015/03/06/five-myths-about-daylight-saving-time/ |access-date=16 March 2022 |issn=0190-8286 |archive-date=13 March 2022 |archive-url=https://web.archive.org/web/20220313163234/https://www.washingtonpost.com/outlook/2015/03/06/five-myths-about-daylight-saving-time/ |url-status=live }}</ref><ref name="Victor-2016">{{Cite news |last=Victor |first=Daniel |date=11 March 2016 |title=Daylight Saving Time: Why Does It Exist? (It's Not for Farming) |language=en-US |work=The New York Times |url=https://www.nytimes.com/2016/03/12/us/daylight-saving-time-farmers.html |access-date=16 March 2022 |issn=0362-4331 |archive-date=15 March 2022 |archive-url=https://web.archive.org/web/20220315215413/http://www.nytimes.com/2016/03/12/us/daylight-saving-time-farmers.html |url-status=live }}</ref><ref name="Klein">{{Cite web |last=Klein |first=Christopher |title=8 Things You May Not Know About Daylight Saving Time |url=https://www.history.com/news/8-things-you-may-not-know-about-daylight-saving-time |access-date=16 March 2022 |website=.History.com |date=9 March 2012 |language=en |archive-date=15 March 2022 |archive-url=https://web.archive.org/web/20220315222444/https://www.history.com/news/8-things-you-may-not-know-about-daylight-saving-time |url-status=live }}</ref> In reality, farmers have been one of the strongest [[lobbying]] groups against DST since it was first implemented.<ref name="Feltman-2015" /><ref name="Victor-2016" /><ref name="Klein" /> The factors that influence farming schedules, such as morning [[dew]] and [[dairy cattle]]'s readiness to be milked, are ultimately dictated by the sun, so the clock change introduces unnecessary challenges.<ref name="Feltman-2015" /><ref name="Klein" /><ref name="Time magazine">{{Cite magazine |title=When Daylight Saving Time Was Year-Round |url=https://time.com/3695333/daylight-saving-time-wwii/ |access-date=16 March 2022 |magazine=Time |language=en |archive-date=16 March 2022 |archive-url=https://web.archive.org/web/20220316200855/https://time.com/3695333/daylight-saving-time-wwii/ |url-status=live }}</ref>

DST was first implemented in the US with the [[Standard Time Act]] of 1918, a wartime measure for seven months during World War I in the interest of adding more daylight hours to conserve energy resources.<ref name="NPR">[https://www.npr.org/templates/story/story.php?storyId=7779875 A Time-Change Timeline] {{Webarchive|url=https://web.archive.org/web/20220316200855/https://www.npr.org/templates/story/story.php?storyId=7779875 |date=16 March 2022 }}, [[National Public Radio]], 8 March 2007</ref><ref name="Time magazine" /> Year-round DST, or "[[War Time]]", was implemented again during World War II.<ref name="NPR"/> After the war, local jurisdictions were free to choose if and when to observe DST until the [[Uniform Time Act]] which standardized DST in 1966.<ref name="NPR" /><ref>{{Cite web |last=Graphics |first=WSJ com News |title=World War I Centenary: Daylight-Saving Time |url=https://online.wsj.com/ww1/daylight-saving-time |access-date=16 March 2022 |website=The Wall Street Journal |language=en |archive-date=18 January 2018 |archive-url=https://web.archive.org/web/20180118111712/http://online.wsj.com/ww1/daylight-saving-time |url-status=dead}}</ref> Permanent daylight saving time was signed into law by [[Richard Nixon|President Richard Nixon]] in January of 1974, but there were complaints of children going to school in the dark and working people commuting and starting their work day in pitch darkness during the winter. By October 1974, [[Gerald Ford|President Gerald Ford]] signed a law repealing year round daylight savings time.<ref>{{cite web |author1=Meilan Solly |title=What Happened the Last Time the U.S. Tried to Make Daylight Saving Time Permanent? |url=https://www.smithsonianmag.com/smart-news/what-happened-the-last-time-the-us-tried-to-make-daylight-saving-time-permanent-180979742/ |website=Smithsonian Magazine |publisher=Smithsonian Institution |access-date=2 November 2025 |archive-url=https://web.archive.org/web/20250801190037/https://www.smithsonianmag.com/smart-news/what-happened-the-last-time-the-us-tried-to-make-daylight-saving-time-permanent-180979742/ |archive-date=1 August 2025 |url-status=live}}</ref>

==Procedure==
{{See also|Daylight saving time by country}}
{{multiple image|align= left|direction= vertical|width= 165|image1= Begin CEST.svg|alt1= Diagram of a clock showing a transition from 02:00 to 03:00|caption1= When DST observation begins, clocks are advanced by one hour during the very early morning.|image2= End CEST.svg|alt2= Diagram of a clock showing a transition from 03:00 to 02:00|caption2= When DST observation ends and standard time observation resumes, clocks are turned back one hour during the very early morning.<br /><br />Specific times of the clock change vary by jurisdiction.}}

The relevant authorities typically schedule clock changes to occur at (or soon after) [[midnight]] and on a weekend, in order to lessen disruption to weekday schedules.<ref>{{cite web |title= Information for visitors |url= http://www.lordhoweisland.info/important-info.htm |publisher= Lord Howe Island Tourism Association |access-date= 20 April 2009 |url-status=dead |archive-url= https://web.archive.org/web/20090503074945/http://www.lordhoweisland.info/important-info.htm |archive-date= 3 May 2009}}</ref> A one-hour change is usual, but twenty-minute and two-hour changes have been used in the past. Notable exceptions today include [[Lord Howe Island]] with a thirty-minute change, and [[Troll (research station)]] that shifts two hours directly between CEST and GMT since 2016.<ref>{{cite web|url=https://www.timeanddate.com/time/zone/antarctica/troll|title=Time Zone & Clock Changes in Troll Station, Antarctica|website=timeanddate.com|access-date=18 October 2023|archive-date=6 August 2019|archive-url=https://web.archive.org/web/20190806070528/https://www.timeanddate.com/time/zone/antarctica/troll|url-status=live}}</ref>
In all countries that observe daylight saving time seasonally (i.e., during summer and not winter), the clock is advanced from standard time to daylight saving time in the spring, and it is turned back from daylight saving time to standard time in the autumn.

For a midnight change in spring, a digital display of local time would appear to jump from 23:59:59.9 to 01:00:00.0. For the same clock in autumn, the local time would appear to repeat the hour preceding midnight, i.e. it would jump from 23:59:59.9 to 23:00:00.0.

In most countries that observe seasonal daylight saving time, clocks revert in winter to [[standard time]].<ref>{{citation |title=Time Zone Abbreviations – Worldwide List |url=https://www.timeanddate.com/time/zones/ |website=timeanddate.com |access-date=14 May 2020 |archive-date=21 August 2018 |archive-url=https://web.archive.org/web/20180821101900/https://www.timeanddate.com/time/zones/ |url-status=live }}</ref><ref>{{cite web |last1=MacRobert |first1=Alan |title=Time in the Sky and the Amateur Astronomer |date=18 July 2006 |url=https://skyandtelescope.org/astronomy-resources/time-in-the-sky-and-the-amateur-astronomer/ |publisher=Sky and Telescope |access-date=14 May 2020 |archive-date=11 July 2020 |archive-url=https://web.archive.org/web/20200711064657/https://skyandtelescope.org/astronomy-resources/time-in-the-sky-and-the-amateur-astronomer/ |url-status=live }}</ref> An exception exists in Ireland, where its winter clock has the same offset ([[UTC+00:00]]) and legal name as that in Britain ([[Greenwich Mean Time]])—but while its summer clock also has the same offset as Britain's ([[UTC+01:00]]), its legal name is confusingly called Irish ''Standard'' Time<ref>{{cite web |title=Standard Time (Amendment) Act, 1971, Section 1 |url=http://www.irishstatutebook.ie/eli/1971/act/17/section/1/enacted/en/html |website=electronic Irish Statute Book |language=en |access-date=3 June 2019 |archive-date=30 October 2013 |archive-url=https://web.archive.org/web/20131030172404/http://www.irishstatutebook.ie/1971/en/act/pub/0017/sec0001.html |url-status=live }}</ref><ref>{{cite web |title=Time Zones in Ireland |url=https://www.timeanddate.com/time/zone/ireland |website=timeanddate.com |access-date=14 May 2020 |archive-date=31 December 2019 |archive-url=https://web.archive.org/web/20191231223351/https://www.timeanddate.com/time/zone/ireland |url-status=live }}</ref> as opposed to [[British Summer Time]].<ref>{{cite web |title=Time Zones in the United Kingdom |url=https://www.timeanddate.com/time/zone/uk |website=timeanddate.com |access-date=14 May 2020 |archive-date=8 July 2020 |archive-url=https://web.archive.org/web/20200708023651/https://www.timeanddate.com/time/zone/uk |url-status=live }}</ref>

Since 2019, [[Time in Morocco|Morocco]] observes daylight saving time every month but [[Ramadan (calendar month)|Ramadan]]. During the holy month (the date of which is determined by the [[lunar calendar]] and thus moves annually with regard to the [[Gregorian calendar]]), the country's civil clocks observe [[Western European Time]] (UTC+00:00, which geographically overlaps most of the nation). At the close of that month, its clocks are turned forward to [[Western European Summer Time]] (UTC+01:00).<ref>{{cite news |last1=Kasraoui |first1=Safaa |title=Morocco to Switch Clocks Back 1 Hour on May 5 for Ramadan |url=https://www.moroccoworldnews.com/2019/04/270773/morocco-gmt-dst-ramadan/ |work=Morocco World News |date=16 April 2019 |access-date=5 June 2019 |archive-date=5 June 2019 |archive-url=https://web.archive.org/web/20190605064137/https://www.moroccoworldnews.com/2019/04/270773/morocco-gmt-dst-ramadan/ |url-status=live }}</ref><ref name="sgg.gov 2018">{{cite press release |title=Release of the Moroccan Official Journal |url=http://www.sgg.gov.ma/Portals/1/BO/2018/BO_6720-bis_Ar.pdf?ver=2018-10-27-101217-477 |language=ar |access-date=31 October 2018 |archive-url=https://web.archive.org/web/20191026141815/http://www.sgg.gov.ma/Portals/1/BO/2018/BO_6720-bis_Ar.pdf?ver=2018-10-27-101217-477 |archive-date=26 October 2019}}</ref><ref>{{cite web |title=Time Zones in Morocco |url=https://www.timeanddate.com/time/zone/morocco |website=timeanddate.com |access-date=15 May 2020 |archive-date=27 June 2020 |archive-url=https://web.archive.org/web/20200627003422/https://www.timeanddate.com/time/zone/morocco |url-status=live }}</ref>

The time at which to change clocks differs across jurisdictions. Members of the [[European Union]] conduct a coordinated change, changing all zones at the same instant, at 01:00 [[Coordinated Universal Time]] (UTC), which means that it changes at 02:00 [[Central European Time]] (CET), equivalent to 03:00 [[Eastern European Time]] (EET). As a result, the time differences across European time zones remain constant.<ref>{{cite web|url= http://www.npl.co.uk/reference/faqs/at-what-time-should-clocks-go-forward-or-back-for-summer-time-faq-time|last= National Physical Laboratory|title= At what time should clocks go forward or back for summer time (FAQ – Time)|date= 31 March 2016|access-date= 17 October 2016|quote= The time at which summer time begins and ends is given in the relevant EU Directive and UK Statutory Instrument as 1&nbsp;am. Greenwich Mean Time (GMT)... All time signals are based on Coordinated Universal Time (UTC), which can be almost one second ahead of, or behind, GMT so there is a brief period in the UK when the directive is not being strictly followed.|archive-url= https://web.archive.org/web/20161011093001/http://www.npl.co.uk/reference/faqs/at-what-time-should-clocks-go-forward-or-back-for-summer-time-faq-time|archive-date= 11 October 2016}}</ref><ref name=Myers /> North America coordination of the clock change differs, in that each jurisdiction changes at each local clock's 02:00, which temporarily creates an imbalance with the next time zone (until it adjusts its clock, one hour later, at 2 am there). For example, [[Mountain Time Zone|Mountain Time]] is for one hour in the spring two hours ahead of [[Pacific Time Zone|Pacific Time]] instead of the usual one hour ahead, and instead of one hour in the autumn, briefly zero hours ahead of Pacific Time.

The dates on which clocks change vary with location and year; consequently, the time differences between regions also vary throughout the year. For example, [[Paris]] (which uses Central European Time) is usually six hours ahead of [[New York City]] (which uses [[Eastern Time Zone|North American Eastern Time]]), except for a few weeks in March and October/November when it is five hours ahead. Paris and [[Santiago]] are six hours apart during the northern summer, four hours during the southern summer, and five hours for a few weeks per year. Since 1996, [[Summer time in Europe|European Summer Time]] has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union.<ref name=Myers /> Starting in 2007, most of the United States and Canada observed DST from the second Sunday in March to the first Sunday in November, almost two-thirds of the year.<ref>{{cite news |author-first= Tom |author-last=Baldwin |date= 12 March 2007 |url= https://www.thetimes.com/uk/environment/article/us-gets-summertime-blues-as-the-clocks-go-forward-3-weeks-early-d5rjglj28bx |title= US gets summertime blues as the clocks go forward 3 weeks early |work= [[The Times]] |location= London |access-date= 2 November 2018 |archive-date= 2 April 2019 |archive-url= https://web.archive.org/web/20190402042747/https://www.thetimes.co.uk/article/us-gets-summertime-blues-as-the-clocks-go-forward-3-weeks-early-d5rjglj28bx |url-status= live }}</ref> Moreover, the beginning and ending dates are roughly reversed between the northern and southern hemispheres because spring and autumn are displaced six months. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in April, with transitions at the local clock's [[24-hour clock#Midnight 00:00 and 24:00|24:00]].<ref>{{cite web |title= Ley Chile - Decreto 224 13-AGO-2022 Ministerio del Interior y Seguridad Pública, Subsecretaría del Interior |date= 13 August 2022 |publisher= Biblioteca del Congreso Nacional de Chile |language= es |url= https://www.bcn.cl/leychile/navegar?i=1179983&f=2022-08-13 |access-date= 25 October 2025}}</ref> In some countries, clocks are governed by regional jurisdictions within the country such that some jurisdictions change and others do not; this is currently the case in Australia, Canada, and the United States.{{sfnp|''Seize the Daylight''|2005|pp=179–180}}<ref>{{cite news|url= https://www.usatoday.com/story/news/nation-now/2017/03/09/arizona-no-daylight-saving-time/98964644/|title= Why Arizona doesn't observe daylight-saving time|newspaper= [[USA Today]]|access-date= 26 August 2017|archive-date= 30 March 2019|archive-url= https://web.archive.org/web/20190330084430/https://www.usatoday.com/story/news/nation-now/2017/03/09/arizona-no-daylight-saving-time/98964644/|url-status= live}}</ref>

From year to year, the dates on which to change clock may also move for political or social reasons. The [[Uniform Time Act of 1966]] formalized the United States' period of daylight saving time observation as lasting six months (it was previously declared locally); this period was extended to seven months in 1986, and then to eight months in 2005.<ref name="Downing 2018">{{cite news |last1=Downing |first1=Michael |title=One Hundred Years Later, the Madness of Daylight Saving Time Endures |url=http://theconversation.com/100-years-later-the-madness-of-daylight-saving-time-endures-93048 |access-date=14 May 2020 |publisher=The Conversation |date=2018 |archive-date=19 February 2020 |archive-url=https://web.archive.org/web/20200219193534/http://theconversation.com/100-years-later-the-madness-of-daylight-saving-time-endures-93048 |url-status=live }}</ref><ref name="Korch 2015">{{cite news |last1=Korch |first1=Travers |title=The Financial History of Daylight Saving |url=http://www.bankrate.com/finance/personal-finance/financial-history-daylight-saving-1.aspx |access-date=14 May 2020 |publisher=Bankrate |date=2015 |archive-date=11 July 2020 |archive-url=https://web.archive.org/web/20200711014802/https://www.bankrate.com/finance/personal-finance/financial-history-daylight-saving-1.aspx |url-status=live }}</ref><ref>{{cite web |title= Energy Policy Act of 2005, Public Law 109-58 §&nbsp;110 |url= http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=109_cong_public_laws&docid=f:publ058.109 |date= 8 August 2005 |access-date= 11 July 2007 |archive-date= 16 July 2009 |archive-url= https://web.archive.org/web/20090716041640/http://frwebgate.access.gpo.gov/cgi-bin/getdoc.cgi?dbname=109_cong_public_laws&docid=f:publ058.109 |url-status= live }}</ref> The 2005 extension was motivated in part by lobbyists from the candy industry, seeking to increase profits by including [[Halloween]] (31 October) within the daylight saving time period.<ref>{{cite news |last1=Morgan |first1=Thad |title=The Sweet Relationship Between Daylight Saving Time and Halloween |url=http://www.history.com/news/the-sweet-relationship-between-daylight-saving-time-and-halloween |access-date=14 May 2020 |publisher=History |date=2017 |ref=Morgan 2017 |archive-date=12 May 2020 |archive-url=https://web.archive.org/web/20200512163136/http://www.history.com/news/the-sweet-relationship-between-daylight-saving-time-and-halloween }}</ref> In recent history, Australian state jurisdictions not only changed at different local times but sometimes on different dates. For example, in 2008 most states there that observed daylight saving time changed clocks forward on 5 October, but [[Western Australia]] changed on 26 October.<ref>{{cite web |url= http://www.bom.gov.au/climate/averages/tables/dst_times.shtml |title= Implementation dates of daylight saving time within Australia |publisher= Bureau of Meteorology |date= 22 September 2009 |access-date= 11 July 2007 |archive-date= 4 April 2016 |archive-url= https://web.archive.org/web/20160404124201/http://www.bom.gov.au/climate/averages/tables/dst_times.shtml |url-status= live }}</ref>

== Politics, religion and sports ==
The concept of daylight saving has caused controversy since its early proposals.<ref name="Downing-Prerau">DST practices and controversies:
* {{harvp|''Spring Forward''|2005}}
* {{harvp|''Seize the Daylight''|2005}}</ref> [[Winston Churchill]] argued that it enlarges "the opportunities for the pursuit of health and happiness among the millions of people who live in this country"<ref>{{cite journal |author-first= Winston S. |author-last=Churchill |title= A silent toast to William Willett |journal= Pictorial Weekly |date= 28 April 1934 }}</ref> and pundits have dubbed it "Daylight Slaving Time".{{sfnp|''Seize the Daylight''|2005|p=117}} Retailing, sports, and tourism interests have historically favored daylight saving, while agricultural and evening-entertainment interests (and some religious groups{{sfnp|''Seize the Daylight''|2005|pp=[https://archive.org/details/seizedaylightcur0000prer/page/106/mode/1up?q="God's time" 106], [https://archive.org/details/seizedaylightcur0000prer/page/135/mode/1up?q=%22God's+time%22 135], [https://archive.org/details/seizedaylightcur0000prer/page/154/mode/1up?q=%22God's+time%22 154], [https://archive.org/details/seizedaylightcur0000prer/page/175/mode/1up?q=%22God's+time%22 175]; [https://archive.org/details/seizedaylightcur0000prer/page/208/mode/1up?q="religious" 208]; [https://archive.org/details/seizedaylightcur0000prer/page/212/mode/1up?q="Jews" 212];[https://archive.org/details/seizedaylightcur0000prer/page/221/mode/1up/mode/1up?q="Israel" 221]-222}}<ref name="Israel"/><ref name="JewsUS"/><ref name="Fitzpatrick2019"/>) have opposed it; energy crises and war prompted its initial adoption.{{sfnp|''Seize the Daylight''|2005|p=xi}}

Willett's 1907 proposal illustrates several political issues. It attracted many supporters, including [[Arthur Balfour]], Churchill, [[David Lloyd George]], [[Ramsay MacDonald]], King [[Edward VII]] (who used half-hour DST or "[[Sandringham time]]" at Sandringham), the managing director of [[Harrods]], and the manager of the National Bank Ltd.<ref>{{cite book |last1=Slattery |first1=Sir Matthew |title=The National Bank, 1835–1970 |date=1972 |publisher=The National Bank |edition=Privately published |url=https://www.natwestgroup.com/heritage/companies/national-bank-ltd.html}}</ref> However, the opposition proved stronger, including Prime Minister [[H. H. Asquith]], [[William Christie (astronomer)|William Christie]] (the [[Astronomer Royal]]), [[George Darwin]], [[Napier Shaw]] (director of the Meteorological Office), many agricultural organizations, and theatre-owners. After many hearings, a parliamentary committee vote narrowly rejected the proposal in 1909. Willett's allies introduced similar bills every year from 1911 through 1914, to no avail.{{sfnp|''Seize the Daylight''|2005|pp= 12–24}} People in the US demonstrated even more skepticism; [[Andrew James Peters|Andrew Peters]] introduced a DST bill to the House of Representatives in May 1909, but it soon died in committee.{{sfnp|''Seize the Daylight''|2005|pp=72–73}}

[[File:Victory-Cigar-Congress-Passes-DST.jpeg|thumb|upright|alt= Poster titled "VICTORY! CONGRESS PASSES DAYLIGHT SAVING BILL" showing Uncle Sam turning a clock to daylight saving time as a clock-headed figure throws his hat in the air. The clock face of the figure reads "ONE HOUR OF EXTRA DAYLIGHT". The bottom caption says "Get Your Hoe Ready!"| Retailers generally favor DST; [[United Cigar Stores]] hailed a 1918 DST bill.]]

Germany and [[Central Powers|its allies]] led the way in introducing DST during [[World War I]] on 30 April 1916, aiming to alleviate hardships due to wartime coal shortages and air-raid blackouts. The political equation changed in other countries; the United Kingdom used DST first on 21 May 1916.{{sfnp|''Seize the Daylight''|2005|pp= 51–70}} US retailing and manufacturing interests—led by [[Pittsburgh]] industrialist Robert Garland—soon began lobbying for DST, but railroads opposed the idea. The US' 1917 entry into the war overcame objections, and DST started in 1918.{{sfnp|''Seize the Daylight''|2005|pp= 80–101}}

The end of World War I brought a change in DST use. Farmers continued to dislike DST, and many countries repealed it—like Germany itself, which dropped DST from 1919 to 1939 and from 1950 to 1979.<ref>{{cite web|url= https://www.timeanddate.com/time/zone/germany/berlin|title= Time Changes in Berlin Over the Years|website= timeanddate.com|access-date= 27 May 2019|archive-date= 27 May 2019|archive-url= https://web.archive.org/web/20190527010139/https://www.timeanddate.com/time/zone/germany/berlin|url-status= live}}</ref> Britain proved an exception; it retained DST nationwide but adjusted transition dates over the years for several reasons, including special rules during the 1920s and 1930s to avoid clock shifts on Easter mornings. {{As of | 2009}}, summer time began annually on the last Sunday in March under a [[European Community]] directive, which may be Easter Sunday (as in 2016).<ref name=Myers>{{cite web|author-first= Joseph |author-last=Myers|title= History of legal time in Britain|url= http://jsm28.user.srcf.net/british-time/|date= 17 July 2009}}</ref> In the US, Congress repealed DST after 1919. President [[Woodrow Wilson]]—an avid golfer like Willett—vetoed the repeal twice, but his second veto was overridden.{{sfnp|''Seize the Daylight''|2005|pp=103–110}} Only a few US cities retained DST locally,<ref>{{cite book |author-first= Robert |author-last=Garland |title= Ten years of daylight saving from the Pittsburgh standpoint |year= 1927 |publisher= Carnegie Library of Pittsburgh |oclc= 30022847 |url= http://www.clpgh.org/exhibit/dst.html |url-status= dead |archive-url= https://web.archive.org/web/20060928063039/http://www.clpgh.org/exhibit/dst.html |archive-date= 28 September 2006}}</ref> including New York (so that its financial exchanges could maintain an hour of arbitrage trading with London), and Chicago and [[Cleveland]] (to keep pace with New York).{{sfnp|''Spring Forward''|2005|pp= 47–48}} Wilson's successor as president, [[Warren G. Harding]], opposed DST as a "deception", reasoning that people should instead get up and go to work earlier in the summer. He ordered District of Columbia federal employees to start work at 8 am rather than 9 am during the summer of 1922. Some [[business]]es followed suit, though many others did not; the experiment was not repeated.{{sfnp|''Seize the Daylight''|2005|pp= 115–118}}

Since Germany's adoption of DST in 1916, the world has seen many enactments, adjustments, and repeals of DST, with similar politics involved.<ref>{{cite book |title= Business and its Environment |chapter= The politics of the extension of daylight saving time |author-first= David P. |author-last=Baron |isbn= 978-0-13-187355-1 |publisher= Prentice Hall |year= 2005 |edition= 5th }}</ref> The [[history of time in the United States]] features DST during both [[world wars]], but no standardization of peacetime DST until 1966.{{sfnp|''Seize the Daylight''|2005|pp= 147–155, 175–180}}<ref>{{cite journal |author1= Ian R. Bartky |author2= Elizabeth Harrison |title= Standard and daylight-saving time |journal= Scientific American |volume= 240 |issue= 5 |pages= 46–53 |year= 1979 |issn= 0036-8733 |doi= 10.1038/scientificamerican0579-46|bibcode= 1979SciAm.240e..46B }}</ref> [[St. Paul, Minnesota|St. Paul]] and [[Minneapolis, Minnesota]], kept different clocks for two weeks in May 1965: the capital city decided to switch to daylight saving time, while Minneapolis opted to follow the later date set by state law.<ref>{{Cite web|last= Murray|first= David|title= 'Chaos of time': The history of daylight saving time, why we spring forward|url= https://www.greatfallstribune.com/story/news/2017/11/02/chaos-time-history-daylight-saving-time/827781001/|access-date= 9 November 2020|website= Great Falls Tribune|language= en-US|archive-date= 20 January 2021|archive-url= https://web.archive.org/web/20210120125452/https://www.greatfallstribune.com/story/news/2017/11/02/chaos-time-history-daylight-saving-time/827781001/|url-status= live}}</ref><ref>{{Cite news|date= 5 May 1965|title= Twin cities disagree over daylight savings time, 1965|page= 1|work= St. Cloud Times|url= https://www.newspapers.com/clip/8212127/twin-cities-disagree-over-daylight/|access-date= 9 November 2020|via= [[Newspapers.com]] |archive-date= 10 November 2020|archive-url= https://web.archive.org/web/20201110082951/https://www.newspapers.com/clip/8212127/twin-cities-disagree-over-daylight/|url-status= live}}</ref> In the mid-1980s, [[Clorox]] and [[7-Eleven]] provided the primary funding for the Daylight Saving Time Coalition behind the 1987 extension to US DST. Both senators from [[Idaho]], [[Larry Craig]] and [[Mike Crapo]], voted for it based on the premise that fast-food restaurants sell more French fries (made from Idaho potatoes) during DST.<ref name=Benfield>{{cite book |author-first= James C. |author-last=Benfield |chapter= Statement to the U.S. House, Committee on Science, Subcommittee on Energy |title= Energy Conservation Potential of Extended and Double Daylight Saving Time |date= 24 May 2001 |series= Serial 107-30 |chapter-url= http://commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.HTM#66 |access-date= 11 March 2007 |archive-date= 25 August 2007 |archive-url= https://web.archive.org/web/20070825165703/http://commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.htm |url-status= live }}</ref>

A [[1992 Queensland daylight saving referendum|referendum on the introduction of daylight saving]] took place in [[Queensland, Australia]], in 1992, after a three-year trial of daylight saving. It was defeated with a 54.5% "no" vote, with regional and rural areas strongly opposed, and those in the metropolitan southeast in favor.<ref>{{cite web |url= https://www.ecq.qld.gov.au/__data/assets/pdf_file/0016/1708/1992-Statistical-Returns_Daylight-Saving-Summary.pdf |title= 1992 Queensland Daylight Saving Referendum |access-date= 25 July 2010 |url-status= dead |archive-url= https://web.archive.org/web/20170911195711/https://www.ecq.qld.gov.au/__data/assets/pdf_file/0016/1708/1992-Statistical-Returns_Daylight-Saving-Summary.pdf |archive-date= 11 September 2017}}</ref>

In 2003, the United Kingdom's [[Royal Society for the Prevention of Accidents]] supported a proposal to observe year-round daylight saving time, but it has been opposed by some industries, by some postal workers and farmers, and particularly by those living in the northern regions of the UK.<ref name="RoSPA"/>

In 2005, the Sporting Goods Manufacturers Association and the [[National Association of Convenience Stores]] successfully lobbied for the 2007 extension to US DST.<ref name="Beam">{{cite news |url= https://www.boston.com/news/globe/living/articles/2005/07/26/dim_witted_proposal_for_daylight_time/ |title= Dim-witted proposal for daylight time |work= Boston Globe |author-first= Alex |author-last=Beam |date= 26 July 2005 |access-date= 20 April 2020 |archive-date= 3 March 2016 |archive-url= https://web.archive.org/web/20160303191958/http://www.boston.com/news/globe/living/articles/2005/07/26/dim_witted_proposal_for_daylight_time/ |url-status= live }}</ref>

In December 2008, the [[Daylight Saving for South East Queensland]] (DS4SEQ) political party was officially registered in Queensland, advocating the implementation of a dual-time-zone arrangement for daylight saving in [[South East Queensland]], while the rest of the state maintained standard time.<ref>{{cite web |url= http://www.abc.net.au/news/stories/2008/12/14/2445953.htm |work= ABC News |title= Daylight Saving group launched as new Qld political party |date= 14 December 2008 |access-date= 25 July 2010 |archive-date= 4 January 2009 |archive-url= https://web.archive.org/web/20090104003341/http://www.abc.net.au/news/stories/2008/12/14/2445953.htm }}</ref> DS4SEQ contested the March 2009 Queensland state election with 32 candidates and received one percent of the [[Optional preferential voting|statewide primary vote]], equating to around 2.5% across the 32 electorates contested.<ref>{{cite web |url= http://www.ecq.qld.gov.au/elections/state/state2009/results/summary.html#16 |title= Total Candidates Nominated for Election by Party&nbsp;– 2009 State Election |publisher= Electoral Commission of Queensland (ECQ) |access-date= 19 June 2010 |url-status= dead |archive-url= https://web.archive.org/web/20110226114323/http://www.ecq.qld.gov.au/elections/state/state2009/results/summary.html |archive-date= 26 February 2011}}</ref> After a three-year trial, more than 55% of Western Australians voted against DST in 2009, with rural areas strongly opposed.<ref>{{cite news |author-first= Paige |author-last=Taylor |work= The Australian |date= 18 May 2009 |title= Daylight saving at a sunset out west |url= http://www.theaustralian.com.au/news/nation/daylight-saving-at-a-sunset-out-west/story-e6frg6pf-1225713080046 |access-date= 5 March 2010 |archive-date= 27 October 2011 |archive-url= https://web.archive.org/web/20111027170847/http://www.theaustralian.com.au/news/nation/daylight-saving-at-a-sunset-out-west/story-e6frg6pf-1225713080046 |url-status= live }}</ref> Queensland Independent member [[Peter Wellington]] introduced the [[Daylight Saving for South East Queensland Referendum Act 2010|Daylight Saving for South East Queensland Referendum Bill 2010]] into the Queensland parliament on 14 April 2010, after being approached by the DS4SEQ political party, calling for a referendum at the next state election on the introduction of daylight saving into South East Queensland under a dual-time-zone arrangement.<ref>{{cite news | title = Daylight Saving for South East Queensland Referendum Bill 2010 | date = 14 April 2010 | url = https://www.legislation.qld.gov.au/Bills/53PDF/2010/DaySavSEQRB10_P.pdf | access-date = 25 July 2010 | archive-date = 13 June 2010 | archive-url = https://web.archive.org/web/20100613141903/http://www.legislation.qld.gov.au/Bills/53PDF/2010/DaySavSEQRB10_P.pdf | url-status = live }}</ref> The Queensland parliament rejected Wellington's bill on 15 June 2011.<ref>{{cite news | title = Daylight saving silence 'deafening' | date = 16 June 2011 | url = http://www.brisbanetimes.com.au/queensland/daylight-saving-silence-deafening-20110616-1g4k6.html | access-date = 19 June 2011 | archive-url = https://web.archive.org/web/20110618034521/http://www.brisbanetimes.com.au/queensland/daylight-saving-silence-deafening-20110616-1g4k6.html | archive-date = 18 June 2011 }}</ref>

Russia declared in 2011 that it would stay in DST all year long ([[UTC+4:00]]) and Belarus followed with a similar declaration.<ref>{{cite web |url= http://www.timeanddate.com/news/time/belarus-eternal-dst.html |last= Time and Date |title= Eternal Daylight Saving Time (DST) in Belarus |date= 19 September 2011 |access-date= 20 October 2016 |archive-date= 19 October 2017 |archive-url= https://web.archive.org/web/20171019034933/https://www.timeanddate.com/news/time/belarus-eternal-dst.html |url-status= live }}</ref> (The [[Soviet Union]] had operated under permanent [[Decree time|"summer time"]] from 1930 to at least 1982.) Russia's plan generated widespread complaints due to the dark of winter-time mornings, and thus was abandoned in 2014.<ref>{{cite web| url= https://news.yahoo.com/russia-abandons-round-daylight-saving-time-135222141.html| title= Russia abandons year-round daylight-saving time| publisher= AP| date= 1 July 2014| access-date= 21 October 2014| archive-url= https://web.archive.org/web/20150904045548/http://news.yahoo.com/russia-abandons-round-daylight-saving-time-135222141.html| archive-date= 4 September 2015}}</ref> The country changed its clocks to standard time ([[UTC+3:00]]) on 26 October 2014, intending to stay there permanently.<ref>{{cite web|url= https://www.bbc.co.uk/news/world-europe-29773559|title= Russian clocks go back for last time|publisher= BBC|date= 25 October 2014|access-date= 25 October 2014|archive-date= 26 October 2014|archive-url= https://web.archive.org/web/20141026165046/http://www.bbc.co.uk/news/world-europe-29773559|url-status= live}}</ref>

In the United States, [[Arizona]] (with the exception of the Navajo Nation), [[Hawaii]], and the five populated territories ([[American Samoa]], [[Guam]], [[Puerto Rico]], the [[Northern Mariana Islands]], and the [[US Virgin Islands]]) do not participate in daylight saving time.<ref name="ncsl" /><ref>{{Cite web|title=No DST in Most of Arizona|url=https://www.timeanddate.com/time/us/arizona-no-dst.html|first1=Anne|last1=Buckle|access-date=11 February 2022|website=timeanddate.com|language=en|archive-date=8 March 2022|archive-url=https://web.archive.org/web/20220308160922/https://www.timeanddate.com/time/us/arizona-no-dst.html|url-status=live}}</ref> [[Indiana]] only began participating in daylight saving time as recently as 2006. Between 2018 and 2024, former Florida Republican Senator [[Marco Rubio]] repeatedly filed bills to extend daylight saving time permanently into winter, without success.<ref name="howell-2022" />

Mexico observed summertime daylight saving time starting in 1996. In late 2022, the nation's clocks "fell back" for the last time, in restoration of permanent standard time.<ref name="perlmutter-2022">{{cite news |last1=Perlmutter |first1=Lillian |title=Mexico falls back but won't spring forward as summer time abolished |url=https://www.theguardian.com/world/2022/oct/27/mexico-votes-abolish-summer-time-daylight-savings |access-date=7 January 2023 |work=The Guardian |date=27 October 2022}}</ref>

=== Religion ===
Some religious groups and individuals have opposed DST on religious grounds. For religious Muslims and Jews it makes religious practices such as prayer and fasting more difficult or inconvenient.{{sfnp|''Seize the Daylight''|2005|pp= [https://archive.org/details/seizedaylightcur0000prer/page/212/mode/1up?q="Jews" 212];[https://archive.org/details/seizedaylightcur0000prer/page/221/mode/1up/mode/1up?q="Israel" 221]-222}}<ref name="Israel"/><ref name="JewsUS"/><ref name="Fitzpatrick2019"/>
Some Muslim countries, such as Morocco, have temporarily abandoned DST during Ramadan.<ref name="Fitzpatrick2019">{{Cite news|last= Fitzpatrick|first= Kyle|date= 21 October 2019|title= When do the clocks change around the world? And why?|language= en-GB|work= The Guardian|url= https://www.theguardian.com/news/2019/oct/21/spring-forward-fall-back-who-changes-the-clocks-when-and-why|access-date= 4 December 2020|issn= 0261-3077|quote= Most Islamic countries do not use daylight saving time as during Ramadan it can mean that the evening dinner is delayed till later in the day.|archive-date= 1 November 2020|archive-url= https://web.archive.org/web/20201101041718/https://www.theguardian.com/news/2019/oct/21/spring-forward-fall-back-who-changes-the-clocks-when-and-why|url-status= live}}</ref>

In [[Israel Summer Time|Israel, DST]] has been a point of contention between the religious and secular, resulting in fluctuations over the years, and a shorter DST period than in the EU and US. Religious Jews prefer a shorter DST{{efn|Starting after [[Passover]] and ended before [[Yom Kippur]] (less than 180 days)}} due to DST delaying scheduled [[Shacharit|morning prayers]], thus conflicting with standard working and [[business hours]]. Additionally, DST is ended before [[Yom Kippur]] (a 25-hour fast day starting and ending at sunset, much of which is spent praying in synagogue until the fast ends at sunset) since DST would result in the day ending later, which many feel makes it more difficult.{{efn |Although DST does not affect the duration of the fast, which is 25 hours regardless, many find it easier to start and end earlier rather than later.}}<ref name="Israel">* {{cite news |last1=Stoil |first1=Rebecca Anna |title=Politicians fight over setting the clock back |url=https://www.jpost.com/Israel/Politicians-fight-over-setting-the-clock-back |work=The Jerusalem Post |date=2010 |archive-date=22 March 2022 |access-date=22 March 2022 |archive-url=https://web.archive.org/web/20220322013827/https://www.jpost.com/Israel/Politicians-fight-over-setting-the-clock-back |url-status=live }}
* {{cite news |last1=Cohen |first1=Benyamin |title=Senate passes bill to make daylight saving time permanent, complicating life for observant Jews |url=https://forward.com/fast-forward/484030/senate-passes-bill-daylight-saving-time-permanent-orthodox-jewish-sunset/ |work=The Forward |date=2022 |archive-date=22 March 2022 |access-date=22 March 2022 |archive-url=https://web.archive.org/web/20220322013828/https://forward.com/fast-forward/484030/senate-passes-bill-daylight-saving-time-permanent-orthodox-jewish-sunset/ |url-status=live }}</ref>{{sfnp|''Seize the Daylight''|2005|p=[https://archive.org/details/seizedaylightcur0000prer/page/221/mode/1up?q=Israel 221]}}

In the US, Orthodox Jewish groups have opposed extensions to DST,{{sfnp|''Seize the Daylight''|2005|p=[https://archive.org/details/seizedaylightcur0000prer/page/212/mode/1up?q=jews 212]}} as well as a 2022 bipartisan bill<ref>'''''Congressional Record''. "Sunshine Protection Act of 2021 – Senate Debate and Passage." Vol. 168, no. 46, 15 Mar. 2022, pp. S1165–S1166. U.S. Government Publishing Office. <nowiki>https://www.congress.gov/117/crec/2022/03/15/168/46/CREC-2022-03-15-pt1-PgS1165-5.pdf</nowiki>'''</ref> that would make DST permanent, saying it will "interfere with the ability of members of our community to engage in congregational prayers and get to their places of work on time."<ref name="JewsUS">* {{cite news |last1=Kornbluh |first1=Jacob |author-link1=Jacob Kornbluh |title=Orthodox groups launch uphill battle against daylight saving time bill |url=https://forward.com/news/484265/orthodox-union-jewish-sunshine-protection-act-daylight-saving-time-bill/ |work=The Forward |archive-date=21 March 2022 |access-date=22 March 2022 |archive-url=https://web.archive.org/web/20220321165524/https://forward.com/news/484265/orthodox-union-jewish-sunshine-protection-act-daylight-saving-time-bill/ |url-status=live }}
* {{cite news |last1=Berman |first1=Jesse |title=What permanent daylight saving time could mean for the Jewish community |url=https://www.jewishtimes.com/what-permanent-daylight-saving-could-mean-for-the-jewish-community/ |work=Baltimore Jewish Times |date=18 March 2022 |archive-date=22 March 2022 |access-date=22 March 2022 |archive-url=https://web.archive.org/web/20220322013832/https://www.jewishtimes.com/what-permanent-daylight-saving-could-mean-for-the-jewish-community/ |url-status=live }}</ref>

== Effects ==
{{Main|Analysis of daylight saving time}}

=== Effects on electricity consumption ===
[[File:William-Willett.jpg|thumb|right|upright|alt=A standing man in three-piece suit, facing camera. He is about 60 and is bald with a mustache. His left hand is in his pants pocket, and his right hand is in front of his chest, holding his pocket watch.|[[William Willett]] independently proposed DST in 1907 and advocated it tirelessly.{{sfnp|''Seize the Daylight''|2005|p=22}}]]
Proponents of DST generally argue that it saves energy, promotes outdoor leisure activity in the evening (in summer), and is therefore good for physical and psychological health,<ref>{{cite journal | vauthors = Goodman, A, Page, A, Cooper, A | title = Daylight saving time as a potential public health intervention: an observational study of evening daylight and objectively-measured physical activity among 23,000 children from 9 countries|journal = International Journal of Behavioral Nutrition and Physical Activity| date = 23 October 2014| volume = 11| article-number = 84| doi = 10.1186/1479-5868-11-84| pmid = 25341643| pmc = 4364628| s2cid = 298351| doi-access = free}}</ref> reduces traffic accidents, reduces crime or is good for business.<ref name="CBC News-2020">{{Cite news|title=Tired of turning clocks forward and back? You have big business to thank|language=en-US|work=CBC News|url=https://www.cbc.ca/news/business/daylight-saving-business-energy-1.3485281|access-date=4 December 2020|archive-date=4 December 2020|archive-url=https://web.archive.org/web/20201204142613/https://www.cbc.ca/news/business/daylight-saving-business-energy-1.3485281|url-status=live}}</ref> Opponents argue the actual energy savings are inconclusive.<ref>{{Citation| last=Choi| first=Charles| year=2009| title=Does Daylight Saving Time Conserve Energy?| publisher=Scientific American| publication-place =New York, NY, USA| url =https://www.scientificamerican.com/article/does-daylight-saving-times-save-energy/| archive-url  =https://web.archive.org/web/20140130232223/https://www.scientificamerican.com/article/does-daylight-saving-times-save-energy/ |archive-date=30 January 2014}}</ref>

Although energy conservation goals still remain under certain conditions,<ref name="Ahuja">{{cite journal|author1=Dilip R. Ahuja|author2=D. P. Sen Gupta|author3=V. K. Agrawal|year=2007|title=Energy savings from advancing the Indian Standard Time by half an hour|url=http://www.currentscience.ac.in/Downloads/article_id_093_03_0298_0302_0.pdf|journal=Current Science|volume=93|issue=3|pages=298–302|access-date=20 August 2013|archive-date=1 February 2014|archive-url=https://web.archive.org/web/20140201233923/http://www.currentscience.ac.in/Downloads/article_id_093_03_0298_0302_0.pdf|url-status=live}}</ref> energy usage patterns have greatly changed since then. In a publication from 2025, based on this change in consumption patterns, such as air conditioning systems, additional consumption is expected to occur more frequently during daylight saving time in the future.<ref name="Neumann">{{cite journal | last1 = Neumann | first1 = Philipp | last2 = Blanckenburg | first2 = Korbininan von | title = What Time Will It Be? A Comprehensive Literature Review on Daylight Saving Time | journal = Time & Society | date = 2025 | article-number = 0961463X241310562 | doi = 10.1177/0961463X241310562 | url = https://journals.sagepub.com/oi/10.1177/0961463X241310562 | access-date = 2 March 2025| url-access = subscription }}</ref> Electricity use is greatly affected by geography, climate, and economics, so the results of a study conducted in one place may not be relevant to another country or climate.<ref name="Aries" /> Nevertheless, while overall electricity usage does not decrease, the evening peak demand is flattened, which in turn has a direct impact on generation costs.<ref name="Neumann"/>

A 2017 meta-analysis of 44 studies found that DST leads to electricity savings of 0.3% during the days when DST applies.<ref name="Havranek">{{Cite journal|last1=Havranek|first1=Tomas|last2=Herman|first2=Dominik|last3=Irsova|first3=Zuzana|date=1 June 2018|title=Does Daylight Saving Save Electricity? A Meta-Analysis|journal=The Energy Journal|language=en-US|volume=39|issue=2|pages=35–61 |doi=10.5547/01956574.39.2.thav|bibcode=2018EnerJ..39...35H |issn=1944-9089|s2cid=58919134}}</ref><ref name="Irsova - Doesn't">{{Cite web|last1=Irsova|first1=Zuzana|last2=Havranek|first2=Tomas|last3=Herman|first3=Dominik|date=2 December 2017|title=Daylight saving saves no energy|url=http://voxeu.org/article/daylight-saving-saves-no-energy|access-date=2 December 2017|website=VoxEU.org|archive-date=3 December 2017|archive-url=https://web.archive.org/web/20171203153846/http://voxeu.org/article/daylight-saving-saves-no-energy|url-status=live}}</ref> Several studies have suggested that DST increases motor fuel consumption,<ref name="Aries">{{cite journal|author1=Myriam B.C. Aries|author2=Guy R. Newsham|year=2008|title=Effect of daylight saving time on lighting energy use: a literature review|url=https://nrc-publications.canada.ca/eng/view/accepted/?id=19fb83b6-0f6b-4d94-a1a9-6854b57c9dfd|journal=Energy Policy|volume=36|issue=6|pages=1858–1866|doi=10.1016/j.enpol.2007.05.021|access-date=25 September 2019|archive-date=26 October 2019|archive-url=https://web.archive.org/web/20191026141756/https://nrc-publications.canada.ca/eng/view/accepted/?id=19fb83b6-0f6b-4d94-a1a9-6854b57c9dfd|url-status=live}}</ref> but a 2008 [[United States Department of Energy]] report found no significant increase in motor gasoline consumption due to the 2007 United States extension of DST.<ref name="DOE-2008">{{cite report|url=http://www1.eere.energy.gov/analysis/pdfs/epact_sec_110_edst_report_to_congress_2008.pdf|title=Impact of Extended Daylight Saving Time on national energy consumption: report to Congress, Energy Policy Act of 2005, Section 110|author1=David B. Belzer|author2=Stanton W. Hadley|publisher=US Dept. of Energy|author3=Shih-Miao Chin|archive-url=https://web.archive.org/web/20130518104926/http://www1.eere.energy.gov/analysis/pdfs/epact_sec_110_edst_report_to_congress_2008.pdf|year=2008|archive-date=18 May 2013}}</ref> An early goal of DST was to reduce evening usage of [[incandescent lighting]], once a primary use of electricity.<ref name="Bartlett">{{cite book|author-first=Roscoe G. |author-last=Bartlett|title=Energy Conservation Potential of Extended and Double Daylight Saving Time|date=24 May 2001|series=Serial 107-30|chapter=Statement to the US House, Committee on Science, Subcommittee on Energy|author-link=Roscoe G. Bartlett|chapter-url=http://commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.HTM|access-date=11 March 2007|archive-date=25 August 2007|archive-url=https://web.archive.org/web/20070825165703/http://commdocs.house.gov/committees/science/hsy73325.000/hsy73325_0.htm|url-status=live}}</ref>

===Economic effects===
It has been argued that clock shifts correlate with decreased [[economic efficiency]] and that in 2000, the daylight-saving effect implied an estimated one-day loss of $31 billion on US stock exchanges.<ref>{{cite journal|author1=Mark J. Kamstra|author2=Lisa A. Kramer|author3=Maurice D. Levi|year=2000|title=Losing sleep at the market: the daylight saving anomaly|url=http://homes.chass.utoronto.ca/~lkramer/aer-daylightsaving-reply.pdf|journal=American Economic Review|volume=90|issue=4|pages=1005–1011|citeseerx=10.1.1.714.2833|doi=10.1257/aer.90.4.1005|access-date=27 October 2017|archive-date=21 September 2017|archive-url=https://web.archive.org/web/20170921234625/http://homes.chass.utoronto.ca/~lkramer/aer-daylightsaving-reply.pdf|url-status=live}}</ref> Others have asserted that the observed results depend on methodology<ref>{{cite journal|author-first1=Luisa |author-last1=Müller|author-first2=Dirk |author-last2=Schiereck|author-first3=Marc W. |author-last3=Simpson|author-first4=Christian |author-last4=Voigt|year=2009|title=Daylight saving effect|journal=Journal of Multinational Financial Management|volume=19|issue=2|pages=127–138|doi=10.1016/j.mulfin.2008.09.001}}</ref> and disputed the findings,<ref>{{cite journal|author-first=Michael J. |author-last=Pinegar|year=2002|title=Losing sleep at the market: Comment|journal=American Economic Review|volume=92|issue=4|pages=1251–1256|doi=10.1257/00028280260344786|jstor=3083313|s2cid=16002134}}</ref> though the original authors have refuted points raised by disputers.<ref>{{cite journal|author1=Mark J. Kamstra|author2=Lisa A. Kramer|author3=Maurice D. Levi|year=2002|title=Losing sleep at the market: the daylight saving anomaly: Reply|journal=American Economic Review|volume=92|issue=4|pages=1257–1263|doi=10.1257/00028280260344795|jstor=3083314}}</ref>

=== Effects on health ===
There are measurable adverse effects of clock-shifts on human health.<ref>{{Cite journal |last1=Zhang |first1=H. |last2=Khan |first2=A. |last3=Edgren |first3=G. |last4=Rzhetsky |first4=A. |date=8 June 2020 |title=Measurable health effects associated with the daylight saving time shift. |journal=PLOS Comput. Biol. |volume=16 |issue=6 |article-number=e1007927 |doi=10.1371/journal.pcbi.1007927|pmid=32511231 |pmc=7302868 |bibcode=2020PLSCB..16E7927Z |doi-access=free }}</ref> It has been shown to disrupt human [[circadian rhythm]]s,<ref>{{Cite journal |last1=Rishi |first1=M. A. |last2=Ahmed |first2=O. |last3=Barrantes Perez |first3=J. H. |last4=Berneking |first4=J. |last5=Flynn-Evans |first5=E. E. |last6=Gurubhagavatula |first6=I. |title=Daylight saving time: an American Academy of Sleep Medicine position statement |journal=Journal of Clinical Sleep Medicine |year=2020 |volume=16 |issue=10 |pages=1781–1784|doi=10.5664/jcsm.8780 |pmid=32844740 |pmc=7954020 }}</ref> negatively affecting human health in the process,<ref name="Roenneberg June 2019">{{cite journal|vauthors=Roenneberg T, Wirz-Justice A, Skene DJ, Ancoli-Israel S, Wright KP, Dijk DJ, Zee P, Gorman MR, Winnebeck EC, Klerman EB|date=2019|title=Why Should We Abolish Daylight Saving Time?|journal=Journal of Biological Rhythms|volume=34|issue=3|pages=227–230|doi=10.1177/0748730419854197|pmc=7205184|pmid=31170882|doi-access=free}}</ref> and that the yearly DST clock-shifts can increase health risks such as heart attacks<ref name="NatGeo Time" /> and traffic accidents.<ref>{{Cite journal |last1=Fritz |first1=Josef |last2=VoPham |first2=Trang |last3=Wright |first3=Kenneth P. |last4=Vetter |first4=Céline |date=February 2020 |title=A Chronobiological Evaluation of the Acute Effects of Daylight Saving Time on Traffic Accident Risk |journal=Current Biology |volume=30 |issue=4 |pages=729–735.e2 |doi=10.1016/j.cub.2019.12.045 |pmid=32008905 |s2cid=210956409 |issn=0960-9822|doi-access=free |bibcode=2020CBio...30E.729F }}</ref><ref>{{Cite journal |last1=Orsini|first1=Federico|last2=Zarantonello|first2=Lisa|last3=Costa|first3=Rodolfo |last4=Rossi|first4=Riccardo |last5=Montagnese|first5=Sara| date=July 2022 |title=Driving simulator performance worsens after the Spring transition to Daylight Saving Time |journal=iScience |volume=25 |issue=7 |article-number=104666 |doi=10.1016/j.isci.2022.104666 |pmid=35811844 |pmc=9263509 |bibcode=2022iSci...25j4666O |issn=2589-0042}}</ref>

A 2017 study in the ''[[American Economic Journal|American Economic Journal: Applied Economics]]'' estimated that "the transition into DST caused over 30 deaths at a social cost of $275 million annually", primarily by increasing sleep deprivation.<ref>{{Cite journal |last=Smith |first=Austin C. |date=2016 |title=Spring Forward at Your Own Risk: Daylight Saving Time and Fatal Vehicle Crashes |journal=American Economic Journal: Applied Economics |language=en |volume=8 |issue=2 |pages=65–91 |citeseerx=10.1.1.676.1062 |doi=10.1257/app.20140100 |issn=1945-7782}}</ref>

An LSE study found that DST transition increases people's feeling of being rushed for time, and  the number of hours spent on leisure decreases by roughly 10 minutes following the transition and more specifically the spring transition into DST decreases life satisfaction by around 1.44 per cent. They show that respondents are running on less sleep that first day, and their individual productivity is affected as a result.<ref>{{cite web |last1=Costa-i-Font |first1=Joan |title=Are we underestimating the costs of daylight saving time? |url=https://www.lse.ac.uk/research/research-for-the-world/health/end-daylight-saving-time |website=The London School of Economics and Political Science |access-date=1 October 2025 |language=en |date=19 March 2024}}</ref>

A correlation between clock shifts and increase in traffic collisions has been observed in North America and the UK but not in Finland or Sweden.<ref>{{cite journal |last1=Fritz |first1=Josef |date=2020 |title=A Chronobiological Evaluation of the Acute Effects of Daylight Saving Time on Traffic Accident Risk |journal=Current Biology |volume=30 |issue=4 |pages=729–735.e2 |doi=10.1016/j.cub.2019.12.045 |pmid=32008905 |doi-access=free |bibcode=2020CBio...30E.729F |s2cid=210956409}}</ref> Four reports have found that this effect is smaller than the overall reduction in traffic fatalities.<ref>{{cite journal |author1=Jason Varughese |author2=Richard P. Allen |year=2001 |title=Fatal accidents following changes in daylight savings time: the American experience |journal=Sleep Medicine |volume=2 |issue=1 |pages=31–36 |doi=10.1016/S1389-9457(00)00032-0 |pmid=11152980}}</ref><ref>{{cite journal |author1=J. Alsousoua |author2=T. Jenks |author3=O. Bouamra |author4=F. Lecky |author5=K. Willett |year=2009 |title=Daylight savings time (DST) transition: the effect on serious or fatal road traffic collision related injuries |journal=Injury Extra |volume=40 |issue=10 |pages=211–212 |doi=10.1016/j.injury.2009.06.241 |doi-access=free}}</ref><ref>
{{cite journal |author1=Tuuli A. Lahti |author2=Jari Haukka |author3=Jouko Lönnqvist |author4=Timo Partonen |year=2008 |title=Daylight saving time transitions and hospital treatments due to accidents or manic episodes |journal=BMC Public Health |volume=8 |article-number=74 |doi=10.1186/1471-2458-8-74 |pmc=2266740 |pmid=18302734 |doi-access=free }}</ref><ref>{{cite journal |author1=Mats Lambe |author2=Peter Cummings |year=2000 |title=The shift to and from daylight savings time and motor vehicle crashes |journal=Accident Analysis & Prevention |volume=32 |issue=4 |pages=609–611 |doi=10.1016/S0001-4575(99)00088-3 |pmid=10868764}}</ref> According to data shared by Titan Casket, hospitals see a 24% increase in heart attacks<ref>{{Cite journal |last1=Sandhu |first1=Amneet |last2=Seth |first2=Milan |last3=Gurm |first3=Hitinder S. |date=1 March 2014 |title=Daylight savings time and myocardial infarction |journal=Open Heart |language=en |volume=1 |issue=1 |article-number=e000019 |doi=10.1136/openhrt-2013-000019 |issn=2053-3624 |pmc=4189320 |pmid=25332784}}</ref> and a 6% increase in fatal crashes<ref>{{Cite journal |last1=Fritz |first1=Josef |last2=VoPham |first2=Trang |last3=Wright Jr. |first3=Kenneth P. |last4=Vetter |first4=Céline |date=30 January 2020 |title=A Chronobiological Evaluation of the Acute Effects of Daylight Saving Time on Traffic Accident Risk |journal=Current Biology |volume=30 |issue=4 |pages=729–735.e2 |bibcode=2020CBio...30E.729F |doi=10.1016/j.cub.2019.12.045 |pmid=32008905 |doi-access=free}}</ref> each year when the time changes. In 2018, the [[European Parliament]], reviewing a possible abolition of DST, approved a more in-depth evaluation examining the disruption of the human body's circadian rhythms which provided evidence suggesting the existence of an association between DST clock-shifts and a modest increase of occurrence of acute myocardial infarction, especially in the first week after the spring shift.<ref>{{Cite journal |last1=Manfredini |first1=F. |last2=Fabbian |first2=F. |last3=Cappadona |first3=R. |date=2018 |title=Daylight saving time, circadian rhythms, and cardiovascular health |journal=Internal and Emergency Medicine |volume=13 |issue=5 |pages=641–646 |doi=10.1007/s11739-018-1900-4|pmid=29971599 |pmc=6469828 }}</ref> However a Netherlands study found, against the majority of investigations, contrary or minimal effect.<ref>{{Cite journal |last1=Derks |first1=L. |last2=Houterman |first2=S. |last3=Geuzebroek |first3=G.S.C. |title=Daylight saving time does not seem to be associated with number of percutaneous coronary interventions for acute myocardial infarction in the Netherlands |journal=Netherlands Heart Journal |year=2021 |volume=29 |issue=9 |pages=427–432 |doi=10.1007/s12471-021-01566-7|pmid=33765223 |pmc=8397810 }}</ref> Year-round standard time (not year-round DST) is proposed by some to be the preferred option for public health and safety.<ref name="The Globe and Mail">{{cite news|last1=Cermakian|first1=Nicolas|title=Turn back the clock on Daylight Savings: Why Standard Time all year round is the healthy choice|url=https://www.theglobeandmail.com/opinion/article-turn-back-the-clock-on-daylight-savings-why-standard-time-all-year/|newspaper=The Globe and Mail|date=2 November 2019|access-date=4 March 2020|archive-date=20 October 2020|archive-url=https://web.archive.org/web/20201020004547/https://www.theglobeandmail.com/opinion/article-turn-back-the-clock-on-daylight-savings-why-standard-time-all-year/|url-status=live}}</ref><ref name="The Sacramento Bee">{{cite web|last1=Block|first1=Gene|title=Who wants to go to work in the dark? Californians need Permanent Standard Time|date=28 February 2019 |url=https://chancellor.ucla.edu/writings-speeches/wants-go-work-dark-californians-need-permanent-standard-time/|publisher=The Sacramento Bee|access-date=4 March 2020|archive-date=4 March 2020|archive-url=https://web.archive.org/web/20200304052801/https://chancellor.ucla.edu/writings-speeches/wants-go-work-dark-californians-need-permanent-standard-time/|url-status=live}}</ref><ref name="U Calgary News">{{cite web|last1=Antle|first1=Michael|title=Circadian rhythm expert argues against permanent daylight saving time|date=30 October 2019|url=https://www.ucalgary.ca/news/circadian-rhythm-expert-argues-against-permanent-daylight-saving-time|publisher=U Calgary News|access-date=4 March 2020|archive-date=4 March 2020|archive-url=https://web.archive.org/web/20200304052759/https://www.ucalgary.ca/news/circadian-rhythm-expert-argues-against-permanent-daylight-saving-time|url-status=live}}</ref><ref name="CBC News">{{cite news|date=31 October 2019|title=Year-round daylight time will cause 'permanent jet lag,' sleep experts warn in letter to government|publisher=CBC News|url=https://www.cbc.ca/news/canada/british-columbia/daylight-time-bc-sleep-experts-1.5342620|access-date=4 March 2020|archive-date=8 March 2021|archive-url=https://web.archive.org/web/20210308200121/https://www.cbc.ca/news/canada/british-columbia/daylight-time-bc-sleep-experts-1.5342620|url-status=live}}</ref><ref>{{cite journal|last1=Barnes|first1=Christopher M.|last2=Drake|first2=Christopher L.|date=November 2015|title=Prioritizing Sleep Health|journal=Perspectives on Psychological Science|volume=10|issue=6|pages=733–737|doi=10.1177/1745691615598509|pmid=26581727|doi-access=free}}</ref> Clock shifts were found to increase the risk of heart attack by 10 percent,<ref name="NatGeo Time" /> and to disrupt sleep and reduce its efficiency.<ref name="Lahti">{{cite journal|author1=Tuuli A. Lahti|author2=Sami Leppämäki|author3=Jouko Lönnqvist|author4=Timo Partonen|year=2008|title=Transitions into and out of daylight saving time compromise sleep and the rest–activity cycles|journal=BMC Physiology|volume=8|article-number=3|doi=10.1186/1472-6793-8-3|pmc=2259373|pmid=18269740 |doi-access=free }}</ref> Effects on seasonal adaptation of the [[circadian rhythm]] can be severe and last for weeks.<ref>DST and circadian rhythm:
*{{cite journal|author1=Pablo Valdez|author2=Candelaria Ramírez|author3=Aída García|year=2003|title=Adjustment of the sleep–wake cycle to small (1–2h) changes in schedule|journal=Biological Rhythm Research|volume=34|issue=2|pages=145–155|doi=10.1076/brhm.34.2.145.14494|bibcode=2003BioRR..34..145V |s2cid=83648787}}
*{{cite journal|author1=Thomas Kantermann|author2=Myriam Juda|author3=Martha Merrow|author4=Till Roenneberg|author4-link=Till Roenneberg|year=2007|title=The human circadian clock's seasonal adjustment is disrupted by daylight saving time|url=https://pure.rug.nl/ws/files/6711968/2007CurrBiolKantermann.pdf|journal=Current Biology|volume=17|issue=22|pages=1996–2000|doi=10.1016/j.cub.2007.10.025|pmid=17964164|bibcode=2007CBio...17.1996K|s2cid=3135927|access-date=6 June 2020|archive-date=16 November 2020|archive-url=https://web.archive.org/web/20201116060505/https://pure.rug.nl/ws/files/6711968/2007CurrBiolKantermann.pdf|url-status=live}}
*{{cite news |date=25 October 2007 |title=Daylight saving hits late risers hardest |work=ABC News |location=Australia |url=http://www.abc.net.au/science/news/stories/2007/2070223.htm |archive-date=3 December 2019 |access-date=13 February 2009 |archive-url=https://web.archive.org/web/20191203212547/http://www.abc.net.au/science/news/stories/2007/2070223.htm |url-status=live }}</ref>

In 2025, a Stanford study compared the year-long circadian health impact of permanent Standard Time, permanent Daylight Saving Time, and biannually switching in the continental U.S. using models of the human circadian rhythm and health data from the CDC Places dataset. Researchers found that switching to permanent Standard Time was predicted to reduce cases of obesity by 2.6 million cases and stroke by 300,000 cases. Permanent Daylight Saving Time also reduced cases but to a lesser extent. In interviews, the authors caution that this work is from a circadian health perspective and that other factors should be considered in policy decisions such as economic and safety impacts of time policy.<ref>{{Cite journal |last1=Weed |first1=Lara |last2=Zeitzer |first2=Jamie M. |date=2025-09-23 |title=Circadian-informed modeling predicts regional variation in obesity and stroke outcomes under different permanent US time policies |journal=Proceedings of the National Academy of Sciences |volume=122 |issue=38 |article-number=e2508293122 |doi=10.1073/pnas.2508293122|pmid=40953265 |pmc=12478180 |pmc-embargo-date=March 15, 2026 |doi-access=free }}</ref>

=== Effects on social relations ===
DST hurts prime-time television broadcast ratings,<ref name="Kissell">{{cite news|author-first=Rick |author-last=Kissell|date=20 March 2007|title=Daylight-saving dock ratings|work=Variety|url=https://variety.com/2007/scene/markets-festivals/daylight-saving-dock-ratings-1117961488/|access-date=20 April 2020|archive-date=13 April 2009|archive-url=https://web.archive.org/web/20090413015818/http://variety.com/article/VR1117961488.html?categoryid=1275&cs=1|url-status=live}}</ref><ref name="NatGeo Time" /> [[Drive-in theater|drive-ins]] and other theaters.<ref>{{cite book|author-first=Todd D. |author-last=Rakoff|title=A Time for Every Purpose: Law and the Balance of Life|publisher=Harvard University Press|year=2002|isbn=978-0-674-00910-3|page=26}}</ref> Artificial outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime.<ref>{{cite journal |author1=Rachel Pain |author2=Robert MacFarlane |author3=Keith Turner |author4=Sally Gill |year=2006 |title='When, where, if, and but': qualifying GIS and the effect of streetlighting on crime and fear |journal=Environment and Planning A |volume=38 |issue=11 |pages=2055–2074 |doi=10.1068/a38391 |bibcode=2006EnPlA..38.2055P |s2cid=143511067 |url=https://durham-repository.worktribe.com/output/1604620 }}</ref>

Later sunsets from DST are thought to affect behavior; for example, increasing participation in after-school sports programs or outdoor afternoon sports such as golf, and attendance at professional sporting events.<ref name="Downing-2018">{{Cite news|last=Downing|first=Michael|date=9 March 2018|title=One Hundred Years Later, the Madness of Daylight Saving Time Endures|work=Smithsonian|url=https://www.smithsonianmag.com/history/100-years-later-madness-daylight-saving-time-endures-180968435/|access-date=12 March 2018|quote=Today we know that changing the clocks does influence our behavior. For example, later sunset times have dramatically increased participation in afterschool sports programs and attendance at professional sports events. In 1920, The Washington Post reported that golf ball sales in 1918—the first year of daylight saving—increased by 20 percent.|archive-date=11 March 2018|archive-url=https://web.archive.org/web/20180311215048/https://www.smithsonianmag.com/history/100-years-later-madness-daylight-saving-time-endures-180968435/|url-status=live}}</ref> Advocates of daylight saving time argue that having more hours of daylight between the end of a typical workday and evening induces people to consume other goods and services.<ref>{{cite news|author-first=Dana |author-last=Knight|date=17 April 2006|title=Daylight-saving time becomes daylight-spending time for many businesses|work=Indianapolis Star}}</ref><ref name="CBC News-2020" /><ref>{{Cite news|last=Bradley|first=Barbara|date=3 April 1987|title=For business, Daylight Saving Time is daylight spending time|work=The Christian Science Monitor}}</ref>

In 2022, a publication of three replicating studies of individuals, between individuals, and transecting societies, demonstrated that sleep loss affects the human motivation to help others, which in its [[Functional magnetic resonance imaging|fMRI]] findings is "associated with deactivation of key nodes within the social cognition brain network that facilitates prosociality." Furthermore, they detected, through analysis of over three million real-world charitable donations, that the loss of sleep inflicted by the transition to daylight saving time reduces altruistic giving compared to controls (being states not implementing DST). They conclude that the effects on civil society are "non-trivial".<ref>{{Cite journal |last1=Simon |first1=Eti Ben |last2=Vallat |first2=Raphael |last3=Rossi |first3=Aubrey |last4=Walker |first4=Matthew P. |date=23 August 2022 |title=Sleep loss leads to the withdrawal of human helping across individuals, groups, and large-scale societies |journal=PLOS Biology |language=en |volume=20 |issue=8 |article-number=e3001733 |doi=10.1371/journal.pbio.3001733 |issn=1545-7885 |pmc=9398015 |pmid=35998121 |doi-access=free }}</ref>

Another study, which also examined sleep manipulation due to the shift to daylight saving time in the spring, analyzed archival data from judicial punishment imposed by US federal courts which showed sleep-deprived judges exact more severe penalties.<ref>{{Cite journal |last1=Cho |first1=Kyoungmin |last2=Barnes |first2=Christopher M. |last3=Guanara |first3=Cristiano L. |date=13 December 2016 |title=Sleepy Punishers Are Harsh Punishers |journal=Psychological Science |volume=28 |issue=2 |pages=242–247 |doi=10.1177/0956797616678437 |pmid=28182529 |s2cid=11321574 |issn=0956-7976}}</ref>

=== Inconvenience ===
DST's clock shifts have the disadvantage of complexity. People must remember to change their clocks; this can be time-consuming, particularly for mechanical clocks that cannot be moved backward safely.<ref>{{cite news|url=http://www.recordcourier.com/apps/pbcs.dll/article?AID=/20031024/NEWS/310240104 |work=Record–Courier |date=24 October 2003 |title=Daylight saving time ends Sunday |author-first=Joey |author-last=Crandall |archive-url=https://web.archive.org/web/20120229232157/http://www.recordcourier.com/apps/pbcs.dll/article?AID=%2F20031024%2FNEWS%2F310240104 |archive-date=29 February 2012 }}</ref> People who work across time zone boundaries need to keep track of multiple DST rules, as not all locations observe DST or observe it the same way. The length of the calendar day becomes variable; it is no longer always 24 hours. Disruption to meetings, travel, broadcasts, billing systems, and records management is common, and can be expensive.<ref>{{cite news |author-first=Paul |author-last=McDougall |title=PG&E says patching meters for an early daylight-saving time will cost $38&nbsp;million |work=InformationWeek |url=http://www.informationweek.com/news/internet/showArticle.jhtml?articleID=197700487 |date=1 March 2007 |access-date=13 February 2009 |archive-date=6 December 2008 |archive-url=https://web.archive.org/web/20081206010328/http://www.informationweek.com/news/internet/showArticle.jhtml?articleID=197700487 |url-status=live }}</ref> During an autumn transition from 02:00 to 01:00, a clock shows local times from 01:00:00 through 01:59:59 twice, possibly leading to confusion.<ref>{{cite web |url=http://www.webexhibits.org/daylightsaving/c.html |year=2008 |title=Daylight saving time: rationale and original idea |quote=...&nbsp;Lord Balfour came forward with a unique concern: 'Supposing some unfortunate lady was confined with twins&nbsp;...' |access-date=13 February 2009 |archive-date=9 June 2016 |archive-url=https://web.archive.org/web/20160609015207/http://www.webexhibits.org/daylightsaving/c.html |url-status=live }}</ref>

Many farmers oppose DST, particularly [[dairy farmers]] as the milking patterns of their cows do not change with the time,<ref name="NatGeo Time">{{cite news |author-first=Brian |author-last=Handwerk |date=1 December 2013 |title=Time to Move On? The Case Against Daylight Saving Time |publisher=[[National Geographic News]] |url=http://news.nationalgeographic.com/news/2013/11/131101-when-does-daylight-savings-time-end-november-3-science/ |access-date=9 March 2014 |archive-url=https://web.archive.org/web/20140313140334/http://news.nationalgeographic.com/news/2013/11/131101-when-does-daylight-savings-time-end-november-3-science/ |archive-date=13 March 2014}}</ref><ref name="NFU">{{cite web |title=Should we change the clocks? |url=http://www.nfuonline.com/News/Should-we-change-the-clocks-/ |url-status=dead |archive-url=https://archive.today/20120314021932/http://www.nfuonline.com/News/Should-we-change-the-clocks-/ |archive-date=14 March 2012 |access-date=6 January 2012 |publisher=National Farmers Union}}</ref><ref>{{Cite news|last=Crossen|first=Cynthia|date=6 November 2003|title=Daylight Saving Time Pitted Farmers Against The 'Idle' City Folk|language=en-US|work=[[The Wall Street Journal]]|url=https://www.wsj.com/articles/SB106798569494029700|access-date=4 December 2020|issn=0099-9660|archive-date=28 March 2021|archive-url=https://web.archive.org/web/20210328235545/https://www.wsj.com/articles/SB106798569494029700|url-status=live}}</ref> and others whose hours are set by the sun.<ref name="farming">Effect on those whose hours are set by the sun:
* {{harvp|''Spring Forward''|2005|pp=19–33}}
* {{harvp|''Seize the Daylight''|2005|pp=103–110, 149–151, 198}}</ref> There is concern for schoolchildren who are out in the darkness during the morning due to late sunrises.<ref name="NatGeo Time" />

=== Remediation ===
Some clock-shift problems could be avoided by adjusting clocks continuously<ref>{{cite web |url=http://www.squarefree.com/2006/11/01/continuous-daylight-saving-time/ |title=Continuous daylight saving time |author-first=Jesse |author-last=Ruderman |date=1 November 2006 |access-date=21 March 2007 |archive-date=4 May 2016 |archive-url=https://web.archive.org/web/20160504080610/http://www.squarefree.com/2006/11/01/continuous-daylight-saving-time/ |url-status=live }}</ref> or at least more gradually<ref>{{cite web |url=http://jeppesn.dk/summertime.html |title=Proposal for a finer adjustment of summer time (daylight saving time) |date=28 September 2011 |access-date=28 September 2011 |archive-date=8 October 2011 |archive-url=https://web.archive.org/web/20111008213011/http://jeppesn.dk/summertime.html |url-status=live }}</ref>—for example, Willett at first suggested weekly 20-minute transitions—but this would add complexity and has never been implemented. DST inherits and can magnify the disadvantages of standard time. For example, when reading a [[sundial]], one must compensate for it along with time zone and natural discrepancies.<ref>{{cite book |title=Sundials: Their Theory and Construction |author-first=Albert E. |author-last=Waugh |publisher=Dover |isbn=978-0-486-22947-8 |year=1973 |bibcode=1973sttc.book.....W |url=https://archive.org/details/sundialstheirthe00albe }}</ref> Also, sun-exposure guidelines such as avoiding the sun within two hours of noon become less accurate when DST is in effect.<ref>{{cite journal |journal=Photochemistry and Photobiology |year=1992 |volume=56 |issue=2 |pages=229–234 |title=Atmospheric sun protection factor on clear days: its observed dependence on solar zenith angle and its relevance to the shadow guideline for sun protection |author-first=Leith |author-last=Holloway |doi=10.1111/j.1751-1097.1992.tb02151.x |pmid=1502267 |s2cid=1219032 |url=https://zenodo.org/record/1230779 |access-date=6 June 2020 |archive-date=9 August 2020 |archive-url=https://web.archive.org/web/20200809031254/https://zenodo.org/record/1230779 |url-status=live }}</ref>

==Terminology==
As explained by Richard Meade in the English Journal of the (American) [[National Council of Teachers of English]], the form ''daylight savings time'' (with an "s") was already much more common than the older form ''daylight saving time'' in American English ("the change has been virtually accomplished") in 1978. Nevertheless, dictionaries such as [[Merriam-Webster|Merriam-Webster's]], [[The American Heritage Dictionary of the English Language|American Heritage]], and [[Oxford English Dictionary|Oxford]], which typically describe actual usage instead of prescribing outdated usage (and therefore also list the newer form), still list the older form first. This is because the older form is still very common in print and is preferred by many editors. ("Although ''daylight saving time'' is considered correct, ''daylight savings time'' (with an "s") is commonly used."){{sfnp|''Seize the Daylight''|2005|p=xv}} The first two words are sometimes hyphenated (''daylight-saving(s) time''). Merriam-Webster's also lists the forms '''daylight saving''', '''daylight savings''' (both without "time"), and '''daylight time'''.<ref name=variants>''Daylight saving time'' and its variants:
* {{cite journal |author-first=Richard A. |author-last=Meade |title=Language change in this century |journal=English Journal |year=1978 |volume=67 |issue=9 |pages=27–30 |doi=10.2307/815124 |jstor=815124 }}
* {{cite book |chapter=daylight-saving time |chapter-url=http://education.yahoo.com/reference/dictionary/entry/daylight-saving%20time |editor=Joseph P. Pickett |display-editors=et al |title=The American Heritage Dictionary of the English Language |edition=4th |publisher=Houghton Mifflin |location=Boston |isbn=978-0-395-82517-4 |quote=or ''daylight-savings time'' |year=2000 |url=https://archive.org/details/americanheritage0000unse_a1o7 }}
* {{cite book |chapter=daylight saving time |chapter-url=https://www.merriam-webster.com/dictionary/daylight%20saving%20time |title=Merriam–Webster's Online Dictionary |access-date=25 October 2025 |quote=called also ''daylight saving'', ''daylight savings'', ''daylight savings time'', ''daylight time''}}
* {{cite web|url=http://www.oxforddictionaries.com/us/definition/american_english/daylight-saving-time|title=daylight saving time|work=Oxford Dictionaries|access-date=22 March 2014|archive-date=22 March 2014|archive-url=https://web.archive.org/web/20140322225739/http://www.oxforddictionaries.com/us/definition/american_english/daylight-saving-time}} "also daylight savings time"
* {{cite web |title=15 U.S.C. §&nbsp;260a notes |url=https://www.law.cornell.edu/uscode/text/15/260a- |access-date=9 May 2007 |quote=Congressional Findings; Expansion of Daylight Saving Time |archive-date=9 November 2021 |archive-url=https://web.archive.org/web/20211109184456/https://www.law.cornell.edu/uscode/text/15/260a |url-status=live }}</ref> The Oxford Dictionary of American Usage and Style explains the development and current situation as follows:<blockquote>Although the singular form ''daylight saving time'' is the original one, dating from the early 20th century—and is preferred by some usage critics—the plural form is now extremely common in AmE. [...] The rise of ''daylight savings time'' appears to have resulted from the avoidance of a miscue: when ''saving'' is used, readers might puzzle momentarily over whether ''saving'' is a gerund (the saving of daylight) or a participle (the time for saving). [...] Using ''savings'' as the adjective—as in ''savings account'' or ''savings bond''—makes perfect sense. More than that, it ought to be accepted as the better form.<ref>{{cite dictionary|url=https://books.google.com/books?id=z_VmtjAU01YC&pg=PA95|title=daylight saving(s) time|dictionary=Oxford Dictionary of American Usage and Style|page=95|isbn=978-0-19-513508-4|last1=Garner|first1=Bryan A.|year=2000|publisher=Oxford University Press |access-date=6 June 2020|archive-date=9 November 2021|archive-url=https://web.archive.org/web/20211109184533/https://books.google.com/books?id=z_VmtjAU01YC&pg=PA95|url-status=live}}</ref></blockquote>In Britain, Willett's 1907 proposal<ref name="Willett" /> used the term ''daylight saving'', but by 1911, the term ''summer time'' replaced ''daylight saving time'' in draft legislation.{{sfnp|''Seize the Daylight''|2005|p=22}} The same or similar expressions are used in many other languages: ''Sommerzeit'' in German, ''zomertijd'' in Dutch, ''kesäaika'' in Finnish, ''horario de verano'' or ''hora de verano'' in Spanish, and ''heure d'été'' in French.{{sfnp|''Seize the Daylight''|2005|pp=51–70}}

The name of local time typically changes when DST is observed. American English replaces ''standard'' with ''daylight'': for example, ''[[Pacific Time Zone|Pacific Standard Time]]'' (''PST'') becomes ''Pacific Daylight Time'' (''PDT''). In the United Kingdom, the standard term for UK time when advanced by one hour is ''British Summer Time'' (BST), and British English typically inserts ''summer'' into other time zone names, e.g. ''Central European Time'' (''CET'') becomes ''[[Central European Summer Time]]'' (''CEST'').

{{anchor|Mnemonic}}
In North American English, people use the mnemonic "spring forward, fall back" (also "spring ahead&nbsp;...", "spring up&nbsp;...", and "...&nbsp;fall behind") to remember the direction in which to shift the clocks.<ref>{{cite news|url=https://www.newspapers.com/clip/35784382/spring-forward-fall-backbrooklyn/|work=Brooklyn Citizen|date=25 April 1936|title=Remember to Put Clocks Hour Ahead on Retiring|access-date=7 November 2021|archive-date=8 November 2021|archive-url=https://web.archive.org/web/20211108121336/https://www.newspapers.com/clip/35784382/spring-forward-fall-backbrooklyn/|url-status=live}}</ref><ref name="Downing-Prerau" />

==Computing==
[[File:Daylightsavings.svg|thumb|upright|
alt=Strong man in sandals and with shaggy hair, facing away from audience/artist, grabbing a hand of a clock bigger than he is and attempting to force it backwards. The clock uses Roman numerals and the man is dressed in stripped-down Roman gladiator style. The text says "You can't stop time... But you can turn it back one hour at 2 a.m. on Oct. 28 when daylight-saving time ends and standard time begins."|
A 2001 US [[Public service advertising|public service advertisement]] reminded people to adjust clocks.]]

Changes to DST rules cause problems in existing computer installations. For example, the [[Energy Policy Act of 2005#Change to daylight saving time|2007 change to DST rules]] in North America required that many computer systems be upgraded, with the greatest onus on e-mail and calendar programs. The upgrades required a significant effort by corporate [[Information technology|information technologists]].<ref>{{cite news |author-first=Steve |author-last=Lohr |title=Time change a 'mini-Y2K' in tech terms |url=https://www.nytimes.com/2007/03/05/technology/05daylight.html |work=[[The New York Times]] |date=5 March 2007 |access-date=21 February 2017 |archive-date=1 February 2017 |archive-url=https://web.archive.org/web/20170201213854/http://www.nytimes.com/2007/03/05/technology/05daylight.html |url-status=live }}</ref>

Some applications standardize on UTC to avoid problems with clock shifts and time zone differences.<ref>{{cite conference |author1=A. Gut |author2=L. Miclea |author3=Sz. Enyedi |author4=M. Abrudean |author5=I. Hoka |title=Database globalization in enterprise applications |book-title=2006 IEEE International Conference on Automation, Quality and Testing, Robotics |year=2006 |pages=356–359 }}</ref> Likewise, most modern operating systems internally handle and store all times as UTC and only convert to local time for display.<ref>{{cite web |author-first=Ron |author-last=Bean |url=http://tldp.org/HOWTO/Clock-2.html |title=The Clock Mini-HOWTO |date=November 2000 |access-date=10 January 2012 |archive-date=13 January 2012 |archive-url=https://web.archive.org/web/20120113081243/http://tldp.org/HOWTO/Clock-2.html |url-status=live }}</ref><ref>{{cite web |author-first=Raymond |author-last=Chen |url=https://devblogs.microsoft.com/oldnewthing/20040902-00/?p=37983 |title=Why does Windows keep your BIOS clock on local time? |date=November 2000 |access-date=10 January 2012 |archive-date=3 January 2012 |archive-url=https://web.archive.org/web/20120103015240/http://blogs.msdn.com/b/oldnewthing/archive/2004/09/02/224672.aspx |url-status=live }}</ref> However, even if UTC is used internally, the systems still require external [[leap second]] updates and time zone information to correctly calculate local time as needed. Many systems in use today base their date/time calculations from data derived from the [[tz&nbsp;database]] also known as zoneinfo.

===IANA time zone database===
The [[Internet Assigned Numbers Authority]] (IANA) [[tz&nbsp;database]] maps a name to the named location's historical and predicted clock shifts. This database is used by many computer software systems, including most [[Unix-like]] operating systems, [[Java (Sun)|Java]], and the [[Oracle RDBMS]];<ref>{{cite web |author1=Paul Eggert |author2=Arthur David Olson |url=https://data.iana.org/time-zones/tz-link.html |title=Time zone and daylight saving time data}}</ref> [[Hewlett-Packard|HP]]'s "tztab" database is similar but incompatible.<ref>{{cite book |publisher=Hewlett–Packard Co |title=HP-UX Reference: HP-UX 11i Version 3 |chapter-url=http://h20000.www2.hp.com/bc/docs/support/SupportManual/c02271674/c02271674.pdf |chapter=tztab(4) |year=2010 |url-status=dead |archive-url=https://web.archive.org/web/20130921054222/http://h20000.www2.hp.com/bc/docs/support/SupportManual/c02271674/c02271674.pdf |archive-date=21 September 2013 }}</ref> When temporal authorities change DST rules, zoneinfo updates are installed as part of ordinary system maintenance. In Unix-like systems the TZ [[environment variable]] specifies the [[List of tz zones by name|location name]], as in <code>TZ=':America/New_York'</code>. In many of those systems there is also a system-wide setting that is applied if the TZ environment variable is not set: this setting is controlled by the contents of the <code>/etc/localtime</code> file, which is usually a [[symbolic link]] or [[hard link]] to one of the zoneinfo files. Internal time is stored in time-zone-independent [[Unix time]]; the TZ is used by each of potentially many simultaneous users and processes to independently localize time display.

Older or stripped-down systems may support only the TZ values required by [[POSIX]], which specify at most one start and end rule explicitly in the value. For example, <code>TZ='EST5EDT,M3.2.0/02:00,M11.1.0/02:00'</code> specifies time for the eastern United States starting in 2007. Such a TZ value must be changed whenever DST rules change, and the new value applies to all years, mishandling some older timestamps.<ref>{{cite book |url=http://www.unix.org/version3/ |publisher=The Open Group |title=IEEE Std 1003.1–2004 |year=2004 |chapter-url=http://www.opengroup.org/susv3/basedefs/xbd_chap08.html#tag_08_03 |chapter=Other environment variables |access-date=17 February 2007 |archive-date=6 July 2010 |archive-url=https://web.archive.org/web/20100706063716/http://www.unix.org/version3/ |url-status=live }}</ref>

==Opposition to clock changes==
{{See also|Permanent time observation in the United States|Decree time|Summer time in Europe#Future|label2=Decree time in Russia|Daylight saving time in Asia#Asian countries not using DST| Daylight saving time in Brazil}}Opposition to changing the clocks twice a year broadly takes three forms:

* a preference for year-round standard time,
* a preference for year-round daylight saving time, and
* a desire to "lock the clock", regardless of whether the result is year-round standard or year-round daylight time.<ref>{{Cite journal |last=Rubin |first=Rita |date=2023-03-28 |title=Groundswell Grows for Permanent Daylight Saving Time, but Medical Societies Overwhelmingly Support Year-Round Standard Time |url=https://jamanetwork.com/journals/jama/article-abstract/2802477 |journal=JAMA |volume=329 |issue=12 |pages=965–967 |doi=10.1001/jama.2023.0159 |pmid=36884231 |issn=0098-7484 |via=<!-- [[WP:TWL]] --> |url-access=subscription |archive-date=18 March 2025 |access-date=17 March 2025 |archive-url=https://web.archive.org/web/20250318051144/https://jamanetwork.com/journals/jama/article-abstract/2802477 |url-status=live }}</ref><ref>{{Cite book |last=Phillips |first=Rasheedah |url=https://books.google.com/books?id=1REEEQAAQBAJ&dq=%22lock+the+clock%22&pg=RA1-PA62 |title=Dismantling the Master's Clock: On Race, Space, and Time |date=2025-01-28 |publisher=[[AK Press]] |isbn=978-1-84935-562-9 |pages=<!-- no page numbers; URL is set to correct page --> |language=en}}</ref>

[[File:Willett memorial.JPG|thumb|upright|alt=A standing stone in a grassy field surrounded by trees. The stone contains a vertical sundial centered on 1 o'clock, and is inscribed "HORAS NON NUMERO NISI ÆSTIVAS" and "SUMMER TIME ACT 1925"|The [[William Willett]] Memorial Sundial in [[Petts Wood]], south London, is always on DST.]]
A move to permanent daylight saving time (staying on summer hours all year with no clock shifts) is sometimes advocated and is currently implemented in some jurisdictions such as Argentina, Belarus,<ref name=Guardian>{{cite news|last=Parfitt|first=Tom|title=Think of the cows: clocks go forward for the last time in Russia|url=https://www.theguardian.com/world/2011/mar/25/clocks-go-forward-last-time-russia?|access-date=5 January 2012|newspaper=The Guardian|date=25 March 2011|archive-date=27 October 2019|archive-url=https://web.archive.org/web/20191027103418/https://www.theguardian.com/world/2011/mar/25/clocks-go-forward-last-time-russia|url-status=live}}</ref> Iceland, Kyrgyzstan, Morocco,<ref name="sgg.gov 2018" /> Namibia, [[Northern Cyprus]], [[Paraguay]], [[Time in Saskatchewan|Saskatchewan]], Syria, Turkey, Turkmenistan, Uzbekistan, and the [[Yukon]]. Although Saskatchewan follows Central Standard Time, its capital city [[Regina, Saskatchewan|Regina]] experiences solar noon close to 13:00, in effect putting the city on permanent daylight time. Similarly, Yukon is classified as being in the Mountain Time Zone, though in effect it observes permanent Pacific Daylight Time to align with the Pacific time zone in summer, but local solar noon in the capital [[Whitehorse]] occurs nearer to 14:00, in effect putting Whitehorse on "double daylight time".{{citation needed|date=June 2024}}

The United Kingdom and Ireland put clocks forward by an extra hour during World War II and experimented with year-round summer time between 1968 and 1971.<ref>{{cite news|last1=Hollingshead|first1=Iain|url=https://www.theguardian.com/commentisfree/2006/jun/24/comment.mainsection2|work=The Guardian|location=London|date=June 2006|title=Whatever happened to Double Summer Time?|access-date=18 March 2017|archive-date=22 March 2021|archive-url=https://web.archive.org/web/20210322153129/https://www.theguardian.com/commentisfree/2006/jun/24/comment.mainsection2|url-status=live}}</ref> Russia switched to permanent DST from 2011 to 2014, but the move proved unpopular because of the extremely late winter sunrises; in 2014, Russia switched permanently back to standard time.<ref name=Russia>{{cite news|title=Russia set to turn back the clocks with daylight-saving time shift|url=https://www.theguardian.com/world/2014/jul/01/russia-state-duma-daylight-saving-time-summer|access-date=25 October 2014|work=The Guardian|location=London|date=1 July 2014|archive-date=21 December 2016|archive-url=https://web.archive.org/web/20161221105745/https://www.theguardian.com/world/2014/jul/01/russia-state-duma-daylight-saving-time-summer|url-status=live}}</ref> However, the change to permanent DST has proven popular in Turkey, with the Minister of Energy and Natural Resources saying the practice saves "millions in energy costs and reduces depression and anxiety levels associated with short exposure to daylight".<ref name="Daily Sabah 2021">{{cite web | title=Turkey will not turn back the clock for daylight saving time | website=Daily Sabah | date=7 December 2021 | url=https://www.dailysabah.com/turkey/turkey-will-not-turn-back-the-clock-for-daylight-saving-time/news | access-date=20 September 2022}}</ref>

In September 2018, the [[European Commission]] proposed to end seasonal clock changes as of 2019.<ref>{{cite web |title=Press corner |url=https://ec.europa.eu/commission/presscorner/detail/en/MEMO_18_5641 |website=European Commission |access-date=23 October 2020 |language=en |date=12 September 2018 |archive-date=23 October 2020 |archive-url=https://web.archive.org/web/20201023093627/https://ec.europa.eu/commission/presscorner/detail/en/MEMO_18_5641 |url-status=live }}</ref> Member states would have the option of observing either daylight saving time all year round or standard time all year round. In March 2019, the European Parliament approved the commission's proposal, while deferring implementation from 2019 until 2021.<ref>{{cite news |url=https://www.theguardian.com/world/2019/mar/26/european-parliament-votes-to-scrap-daylight-saving-time-from-2021 |title=European parliament votes to scrap daylight saving time from 2021 |date=26 March 2019 |access-date=9 July 2019 |newspaper=The Guardian |location=London |edition=US |archive-date=20 June 2019 |archive-url=https://web.archive.org/web/20190620184806/https://www.theguardian.com/world/2019/mar/26/european-parliament-votes-to-scrap-daylight-saving-time-from-2021 |url-status=live }}</ref> In response to this proposition, the European Sleep Research Society stated "installing permanent Central European Time (CET, standard time or 'wintertime') is the best option for public health."<ref>{{cite web | url = https://esrs.eu/wp-content/uploads/2019/03/To_the_EU_Commission_on_DST.pdf | date = March 2019 | title = To the EU Commission on DST | access-date = 4 November 2021 | archive-date = 30 December 2020 | archive-url = https://web.archive.org/web/20201230052703/https://esrs.eu/wp-content/uploads/2019/03/To_the_EU_Commission_on_DST.pdf | url-status = live }}</ref> {{As of|2020|October}}, the decision has not been confirmed{{Fix|text=Needs update}} by the Council of the European Union.<ref>{{cite web |title=Seasonal clock change in the EU |url=https://ec.europa.eu/transport/themes/summertime_en |website=Mobility and Transport – European Commission |access-date=23 October 2020 |language=en |date=22 September 2016 |archive-date=30 June 2019 |archive-url=https://web.archive.org/web/20190630055330/https://ec.europa.eu/transport/themes/summertime_en |url-status=live }}</ref> The council has asked the commission to produce a detailed assessment of its effects, but the Commission considers that the onus is on the Member States to find a common position in Council.<ref>{{cite news |last1=Posaner |first1=Joshua |last2=Cokelaere |first2=Hanne |title=Stopping the clock on seasonal time changes? Not anytime soon |url=https://www.politico.eu/article/eu-blame-game-over-failure-to-end-clock-change/ |work=Politico |date=24 October 2020 |access-date=26 October 2020 |archive-date=26 October 2020 |archive-url=https://web.archive.org/web/20201026084133/https://www.politico.eu/article/eu-blame-game-over-failure-to-end-clock-change/ |url-status=live }}</ref> As a result, progress on the issue is effectively blocked.<ref>{{cite news |last1=Lawson |first1=Patrick |title=The plan to abolish the time change is "completely blocked" at European level, says specialist in European issues |url=https://www.geads.co.uk/2020/10/25/the-plan-to-remove-the-time-change-is-completely-blocked-at-european-level-says-specialist-in-european-issues/ |archive-url= https://web.archive.org/web/20210212075621/https://www.geads.co.uk/2020/10/25/the-plan-to-remove-the-time-change-is-completely-blocked-at-european-level-says-specialist-in-european-issues/|work=Geads News |date=18 November 2020|archive-date=12 February 2021}}</ref>

In the United States, several states have enacted legislation to implement permanent DST, but the bills would require Congress to change federal law in order to take effect. The Uniform Time Act of 1966 permits states to opt out of DST and observe permanent standard time, but it does not permit permanent DST.<ref name="ncsl">{{cite web |title=Daylight Saving Time State Legislation |url=https://www.ncsl.org/research/transportation/daylight-savings-time-state-legislation.aspx |publisher=National Conference of State Legislatures |access-date=3 January 2023 |archive-date=13 April 2020 |archive-url=https://web.archive.org/web/20200413221303/https://www.ncsl.org/research/transportation/daylight-savings-time-state-legislation.aspx |url-status=live }}</ref><ref>{{cite news |url=https://www.usatoday.com/story/news/nation/2018/11/01/daylight-saving-time-ends-sunday-get-ready-fall-back/1846836002/ |title=Fall back! Daylight saving time ends Sunday |work=USA Today |date=1 November 2018 |access-date=2 November 2018 |archive-date=2 November 2018 |archive-url=https://web.archive.org/web/20181102013103/https://www.usatoday.com/story/news/nation/2018/11/01/daylight-saving-time-ends-sunday-get-ready-fall-back/1846836002/ |url-status=live }}</ref> [[Florida]] [[Senate|senator]] [[Marco Rubio]] in particular has promoted changing the federal law to implement permanent DST,<ref>{{Cite web |title=Rubio's Bill to Make Daylight Saving Time Permanent Passes Senate |url=https://www.rubio.senate.gov/public/index.cfm/2022/3/rubio-s-bill-to-make-daylight-saving-time-permanent-passes-senate |access-date=15 June 2022 |website=rubio.senate.gov |date=15 March 2022 |language=en |archive-date=28 June 2022 |archive-url=https://web.archive.org/web/20220628023753/https://www.rubio.senate.gov/public/index.cfm/2022/3/rubio-s-bill-to-make-daylight-saving-time-permanent-passes-senate |url-status=dead }}</ref> with the support of the Florida Chamber of Commerce seeking to boost evening revenue.<ref name="haughey-2020">{{cite news |last1=Haughey |first1=John |title=Time – and money – at stake in Florida-led proposal to extend daylight saving |url=https://www.thecentersquare.com/florida/time-and-money-at-stake-in-florida-led-proposal-to-extend-daylight-saving/article_0a06424c-f9c6-11ea-bbf5-53dce3e5869d.html |access-date=3 January 2023 |work=The Center Square Florida |date=18 September 2022 |quote=The Florida Chamber of Commerce and state business associations maintain an extra hour of sunlight in the winter, during peak tourist season, would translate into more sales. |archive-date=3 January 2023 |archive-url=https://web.archive.org/web/20230103015914/https://www.thecentersquare.com/florida/time-and-money-at-stake-in-florida-led-proposal-to-extend-daylight-saving/article_0a06424c-f9c6-11ea-bbf5-53dce3e5869d.html |url-status=live }}</ref> In 2022, Rubio's "Sunshine Protection Act" passed the United States Senate without committee review by way of [[Voice vote#United States|voice consent]], with many senators afterward stating they were unaware of the vote or its topic.<ref name="mcleod-2022">{{cite news |last1=McLeod |first1=Paul |title=Everyone Was Surprised By The Senate Passing Permanent Daylight Saving Time. Especially The Senators. |url=https://www.buzzfeednews.com/article/paulmcleod/daylight-saving-time-senate |access-date=3 January 2023 |work=BuzzFeed |date=17 March 2022 |archive-date=3 January 2023 |archive-url=https://web.archive.org/web/20230103021303/https://www.buzzfeednews.com/article/paulmcleod/daylight-saving-time-senate |url-status=live }}</ref> The bill was stopped in the US House, where questions were raised as to whether permanent DST or standard time would be more beneficial.<ref name="howell-2022">{{cite news |last1=Howell |first1=Tom Jr. |title=Rubio to keep fighting for permanent daylight saving time after clock runs out for this Congress |url=https://www.washingtontimes.com/news/2022/dec/21/marco-rubio-keep-fighting-permanent-daylight-savin/ |access-date=3 January 2023 |date=21 December 2022}}</ref><ref name="schnell-2022">{{cite news |last1=Schnell |first1=Mychael |title=Permanent daylight saving time hits brick wall in House |url=https://thehill.com/homenews/house/3571007-permanent-daylight-saving-time-hits-brick-wall-in-house/ |access-date=3 January 2023 |work=The Hill |date=25 July 2022 |archive-date=5 April 2024 |archive-url=https://web.archive.org/web/20240405234855/https://thehill.com/homenews/house/3571007-permanent-daylight-saving-time-hits-brick-wall-in-house/ |url-status=live }}</ref> Polling as of 2025 shows a majority of Americans polled now prefer to permanently end DST, with 54% of Americans reporting that a permanent switch to standard time would be preferable. The emergent majority indicates that permanent DST would also be preferred over no change, with the least popular activity being the changing of the time twice per year regardless of DST or standard time being the permanent method of keeping time.<ref name=":0">{{Cite web |last1=Evans |first1=Mary Claire |last2=Jones |first2=Jeffrey M. |date=2025-03-04 |title=More Than Half in U.S. Want Daylight Saving Time Sunsetted |url=https://news.gallup.com/poll/657584/half-daylight-saving-time-sunsetted.aspx |access-date=2025-03-11 |website=[[Gallup, Inc.]] |language=en}}</ref><ref>{{Cite web |last=Tuccille |first=J. D. |date=2025-03-10 |title=We're overdue to end Daylight Saving Time |url=https://reason.com/2025/03/10/were-overdue-to-end-daylight-saving-time/ |access-date=2025-03-11 |website=Reason.com |language=en-US |archive-date=14 March 2025 |archive-url=https://web.archive.org/web/20250314005414/https://reason.com/2025/03/10/were-overdue-to-end-daylight-saving-time/ |url-status=live }}</ref>

Advocates cite the same advantages as normal DST without the problems associated with the twice-yearly clock shifts. Additional benefits have also been cited, including safer roadways, boosting the tourism industry, and energy savings. Detractors cite the relatively late sunrises, particularly in winter, that year-round DST entails.<ref name="Handwerk">{{cite magazine|last= Handwerk|first= Brian|title= Permanent Daylight Saving Time? Might Boost Tourism, Efficiency|url= http://news.nationalgeographic.com/news/travelnews/2011/11/111104-daylight-saving-time-science-travel/|magazine= National Geographic|access-date= 5 January 2012|date= 6 November 2011|archive-date= 9 April 2019|archive-url= https://web.archive.org/web/20190409104629/https://news.nationalgeographic.com/news/travelnews/2011/11/111104-daylight-saving-time-science-travel/}}</ref>

Some experts in circadian rhythms and [[Sleep hygiene|sleep health]] recommend year-round standard time as the preferred option for public health and safety.<ref name="The Globe and Mail"/><ref name="The Sacramento Bee"/><ref name="U Calgary News"/><ref name="CBC News"/> However, some experts state that permanent daylight saving time is still a better option when compared to annual clock changes.<ref>{{Cite web |last=Team |first=The Health News |date=2022-11-04 |title=Is Daylight Saving Time Good or Bad? {{!}} Sharp HealthCare |url=https://www.sharp.com/health-news/the-pros-and-cons-of-permanent-daylight-saving-time-dst |access-date=2024-12-04 |website=www.sharp.com |language=en |archive-date=4 December 2024 |archive-url=https://web.archive.org/web/20241204124110/https://www.sharp.com/health-news/the-pros-and-cons-of-permanent-daylight-saving-time-dst |url-status=live }}</ref><ref name="Kernan 2022">{{cite web | last=Kernan | first=Megan | title=Sleep experts weigh in on Senate approving bill to make Daylight Saving Time permanent | date=18 March 2022 | url=https://www.weau.com/2022/03/18/sleep-experts-weigh-senate-approving-bill-make-daylight-saving-time-permanent/ | access-date=19 September 2022}}</ref> Several [[chronobiology]] societies have published position papers against adopting DST permanently. A paper by the [[Society for Research on Biological Rhythms]] states: "based on comparisons of large populations living in DST or ST or on western versus eastern edges of time zones, the advantages of permanent ST outweigh switching to DST annually or permanently."<ref>{{cite journal | title = Why Should We Abolish Daylight Saving Time? | doi = 10.1177/0748730419854197 | journal = Journal of Biological Rhythms | first1 = Till | last1 = Roenneberg | first2 = Anna | last2 = Wirz-Justice | first3 = Debra J | last3 = Skene | last4 = etc. | date = 6 June 2019 | volume = 34 | issue = 3 | pages = 227–230 | pmid = 31170882 | pmc = 7205184 }}</ref> The World Federation of Societies for Chronobiology recommended "reassigning countries and regions to their actual sun-clock based time zones" and held the position of being "against the switching between DST and Standard Time and even more so against adopting DST permanently."<ref>{{cite journal | title = Daylight Saving Time and Artificial Time Zones – A Battle Between Biological and Social Times | journal = Frontiers in Physiology | first1 = Till | last1 = Roenneberg | first2 = Eva C. | last2 = Winnebeck | first3 = Elizabeth B. | last3 = Klerman | date = 7 August 2019 | volume = 10 | article-number = 944 | doi = 10.3389/fphys.2019.00944 | pmid = 31447685 | pmc = 6692659 | doi-access = free }}</ref> The [[American Academy of Sleep Medicine]] (AASM) holds the position that "seasonal time changes should be abolished in favor of a fixed, national, year-round standard time,"<ref>{{cite journal | date = 15 October 2020 | title = Daylight saving time: an American Academy of Sleep Medicine position statement | journal = J Clin Sleep Med | volume = 16 | issue = 10 | pages = 1781–1784 | first1 = Muhammad Adeel | last1 = Rishi | first2 = Omer | last2 = Ahmed | first3 = Jairo H. | last3 = Barrantes Perez | last4 = etc. | doi = 10.5664/jcsm.8780 | pmid = 32844740 | pmc = 7954020 | s2cid = 221329004 }}</ref> and that "standard time is a better option than daylight saving time for our health, mood and well-being."<ref name="aasm-2022">{{cite web |title=American Academy of Sleep Medicine opposes permanent daylight saving time bill |date=23 May 2022 |url=https://aasm.org/aasm-opposes-permanent-daylight-saving-time-sunshine-protection-act/ |access-date=3 January 2023}}</ref> Their position was endorsed by 20 other organizations, including the [[American College of Chest Physicians]], [[National Safety Council]], and [[Parent–teacher association#United States|National PTA]].<ref name="aasm-2020">{{cite web |title=American Academy of Sleep Medicine calls for elimination of daylight saving time |date=27 August 2020 |url=https://aasm.org/american-academy-of-sleep-medicine-calls-for-elimination-of-daylight-saving-time/ |access-date=3 January 2023 |archive-date=3 January 2023 |archive-url=https://web.archive.org/web/20230103023131/https://aasm.org/american-academy-of-sleep-medicine-calls-for-elimination-of-daylight-saving-time/ |url-status=live }}</ref>

Surveys reported between 2021 and 2022 by the National Sleep Foundation, [[YouGov]], [[CBS]], and [[Monmouth University]] indicate more Americans would prefer permanent DST.<ref>{{Cite web |last=Davies |first=Claire |date=14 March 2021 |title=Sleep Awareness Week 2021: Over 70% say daylight saving time change doesn't affect sleep |url=https://www.toptenreviews.com/sleep-awareness-week-2021-70-say-daylight-savings-change-doesnt-affect-sleep |access-date=11 January 2023 |website=TopTenReviews |language=en}}</ref><ref name="Almanac.com 2023">{{cite web | title=States Object to Changing the Clocks for Daylight Saving Time | website=Almanac.com | date=6 January 2023 | url=https://www.almanac.com/states-object-changing-clocks-daylight-saving-time | access-date=7 January 2023 | archive-date=7 January 2023 | archive-url=https://web.archive.org/web/20230107022009/https://www.almanac.com/states-object-changing-clocks-daylight-saving-time | url-status=dead}}</ref><ref>{{Cite web |title=Daylight Saving Time: Americans want to stay permanently 'sprung forward' and not 'fall back' {{!}} YouGov |url=https://today.yougov.com/topics/politics/articles-reports/2021/11/04/daylight-saving-time-americans-want-stay-permanent |access-date=9 January 2023 |website=today.yougov.com |language=en-us}}</ref> A 2019 survey by the [[NORC at the University of Chicago|National Opinion Research Center]] and a 2021 survey by the [[Associated Press]] indicate more Americans would prefer permanent Standard Time.<ref name="apnorc-2019">{{cite web |title=Daylight Saving Time vs Standard Time |url=https://apnorc.org/projects/daylight-saving-time-vs-standard-time/ |access-date=7 January 2023 |date=2019 |archive-date=7 January 2023 |archive-url=https://web.archive.org/web/20230107171339/https://apnorc.org/projects/daylight-saving-time-vs-standard-time/ |url-status=live }}</ref><ref name="apnorc-2021">{{cite web |title=Dislike for changing the clocks persists |url=https://apnorc.org/projects/dislike-for-changing-the-clocks-persists/ |access-date=7 January 2023 |date=2021 |archive-date=5 January 2023 |archive-url=https://web.archive.org/web/20230105070759/https://apnorc.org/projects/dislike-for-changing-the-clocks-persists/ |url-status=live }}</ref> The National Sleep Foundation, YouGov, and Monmouth University polls leaned significantly in favor of seeing daylight saving time made permanent. The Monmouth University poll reported 44% preferring year-round DST and 13% preferring year-round standard time.<ref name="Almanac.com 2023"/> The [[NORC at the University of Chicago]] found 79% of those interviewed to be in favor of permanent DST during the [[1973 oil crisis|Oil Crisis]] in December 1973; 42% of poll takers supported it the following February.<ref name="ripley-1974">{{cite news |last1=Ripley |first1=Anthony |title=Senate Votes Return to Standard Time For Four Months and Sends Bill to Ford |url=https://www.nytimes.com/1974/10/01/archives/senate-votes-return-to-standard-time-for-four-months-and-sends-bill.html |access-date=7 January 2023 |work=The New York Times |date=1 October 1974 |archive-date=11 June 2020 |archive-url=https://web.archive.org/web/20200611061418/https://www.nytimes.com/1974/10/01/archives/senate-votes-return-to-standard-time-for-four-months-and-sends-bill.html |url-status=live }}</ref>

As of 2025, polls indicate a slight majority of those polled in the United States favor abolishing DST,<ref name=":0" /> with momentum gaining in all areas where the practice persists either to abolish DST and switch permanently to standard time,<ref>{{Cite web |date=2025-03-06 |title=Places around the world that opt out of daylight savings - and why |url=https://www.bbc.com/future/article/20240308-daylight-savings-reasons-history-health-hazards-countries-that-abolished |access-date=2025-03-11 |website=BBC |author-first1=Jennifer |author-last1=Chesak |language=en-GB |archive-date=1 March 2025 |archive-url=https://web.archive.org/web/20250301141724/https://www.bbc.com/future/article/20240308-daylight-savings-reasons-history-health-hazards-countries-that-abolished |url-status=live }}</ref> or to make DST permanent. Common arguments for abolishing or making DST permanent include health risks, economic costs, lost sleep, and disruptions to daily routines.<ref>{{Cite web |date=9 March 2023|title=7 Things to Know About Daylight Saving Time |publisher=Bloomberg School of Public Health, Johns Hopkins University |url=https://publichealth.jhu.edu/2023/7-things-to-know-about-daylight-saving-time#:~:text=Making%20the%20shift%20can%20increase,a%20professor%20in%20Mental%20Health. |access-date=2025-03-11 |language=en|author-first1=Morgan|author-last1=Coulson|url-status=live|archive-url=https://web.archive.org/web/20241225155730/https://publichealth.jhu.edu/2023/7-things-to-know-about-daylight-saving-time|archive-date=25 December 2024}}</ref>

==See also==
* [[Daylight saving time by country]]
** [[Daylight saving time in Africa]]
** [[Daylight saving time in Asia]]
** [[Summer time in Europe]]
** [[Daylight saving time in the Americas]]
*** [[Daylight saving time in the United States]]
*** [[Daylight saving time in Canada]]
** [[Daylight saving time in Oceania]]
* [[Analysis of daylight saving time]]
* [[Winter time (clock lag)]]

==Notes==
{{notelist}}

==References==
{{reflist}}

===Sources===
{{refbegin}}
* {{cite book |author-first=Michael |author-last=Downing |title=Spring Forward: The Annual Madness of Daylight Saving Time |publisher=Shoemaker & Hoard |year=2005 |isbn=978-1-59376-053-3 |ref={{harvid|''Spring Forward''|2005}} |url=https://archive.org/details/springforwardann00down }}
* {{cite book |author-first=David |author-last=Prerau |title=Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time |publisher=Thunder's Mouth Press |year=2005 |isbn=978-1-56025-655-7 |ref={{harvid|''Seize the Daylight''|2005}}|url=https://archive.org/details/seizedaylightcur0000prer }} The British version, focusing on the UK, is {{cite book |title=Saving the Daylight: Why We Put the Clocks Forward |publisher=Granta Books |isbn=978-1-86207-796-6 |author=<!--David Prerau--> |year=<!--2005--> |ref={{harvid|''Saving the Daylight''|2005}}}}
{{refend}}

==Further reading==
* {{cite book |author-first=Ian R. |author-last=Bartky |title= One Time Fits All: The Campaigns for Global Uniformity |publisher= Stanford University Press |year=2007 |isbn=978-0-8047-5642-6}}

==External links==
{{Spoken Wikipedia|Daylight saving time.ogg|date=20 May 2008}}
{{Commons category|Daylight saving time}}
* [https://crsreports.congress.gov/product/pdf/R/R45208/3 Daylight Saving Time] {{Webarchive|url=https://web.archive.org/web/20190322102352/https://crsreports.congress.gov/product/pdf/R/R45208/3 |date=22 March 2019 }} [[Congressional Research Service]]
* [https://www.nist.gov/pml/div688/dst.cfm Information about the Current Daylight Saving Time (DST) Rules], [[National Institute of Standards and Technology|U.S. National Institute of Standards and Technology]]
* [http://www.itu.int/dms_pub/itu-t/opb/sp/T-SP-LT.1-2015-PDF-E.pdf "Legal Time 2015"] {{Webarchive|url=https://web.archive.org/web/20170201213819/http://www.itu.int/dms_pub/itu-t/opb/sp/T-SP-LT.1-2015-PDF-E.pdf |date=1 February 2017 }}, [[ITU-T|Telecommunications Standardization Bureau of the ITU]]
* [https://web.archive.org/web/20120623013511/http://www.twinsun.com/tz/tz-link.htm Sources for time zone and daylight saving time data]
* [https://time.is/DST_2024 Use of Changing Times Around the World]

{{Time measurement and standards}}
{{UTC time offsets}}
{{Daylight Saving Time}}
{{Authority control}}

[[Category:Daylight saving time| ]]