Daylight Saving Time
When we change our clocks
Rationale and original idea
First there was Standard time
Early adoption and U.S. law
Changes and irregularities
Worldwide daylight saving
Worldwide daylight saving
Worldwide daylight saving
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Edited by Michael Douma, see additional credits below.
Supported in part by the U.S. Department of Commerce, National Institute for Standards and Technology (NIST), Time and Frequency Division, as a complement to


You can use the following equations to calculate when DST starts and ends. The divisions are integer divisions, in which remainders are discarded. "mod" means the remainder when doing integer division, e.g., 20 mod 7 = 6. That is, 20 divided by 7 is 2 and 6/7th (where six is the remainder). With: y = year.

For the United States:
Begin DST: Sunday April (2+6*y-y/4) mod 7+1
End DST: Sunday October (31-(y*5/4+1) mod 7)
Valid for years 1900 to 2099, though DST wasn't adopted until the 1950s-1960s.

European Economic Community:
Begin DST: Sunday March (31 - (5*y/4 + 4) mod 7) at 1h U.T.
End DST: Sunday October (31 - (5*y/4 + 1) mod 7) at 1h U.T.
Since 1996, valid through 2099

(Equations by Wei-Hwa Huang (US), and Robert H. van Gent (EC))


Texts are adapted with permission from various sources, as detailed below.

The U.S. Department of Transportation is responsible for overseeing the uniform observance of daylight saving time in the U.S. as well as U.S. time zones. You can obtain further information by e-mailing or by calling (202) 366-9315. Many thanks to Joanne Petrie for help and guidance, and Paul Eggert for corrections.

See original U.S. Laws from 1918 and 1942. Also see an overview of more recent U.S. legislation, and some history in a Congressional Research Report prepared by Heidi Yacker.

Some background information from the introduction to Daylight Saving Time by Curran and Taylor. Also, some information adapted with permission from an article by Bob Aldrich, Information Officer, California Energy Commission; various public sources including "What time is it in Indiana?" from the Monroe County Community School Corporation; articles from the Mining Co and Timechange Creative. Details about standard time from the U.S. Naval Observatory. Thanks to Paul Eggert for assembling historical and current international time zone and daylight saving rules in his archive. Australian information from Australian Daylight Saving Time.

Benjamin Franklin first conceived of Daylight Saving Time in 1784, and published in the Journal de Paris. Read the original text of his proposal, and excerpts and commentary adapted from Keith C. Heidorn in Living Gently Quarterly. It has been reported on this web site, and others, that Franklin wrote about Daylight Saving in his essay "Turkey vs. Eagle, McCauley is my Beagle." We have not found the full text of this essay. There is a different essay to his daughter Sarah which discusses the eagle and the turkey, which was written to his daughter, but it does not discuss daylight saving. That essay can be found in volume 10 of The Writings of Benjamin Franklin, edited by Albert Henry Smyth (NY: The Macmillan Company, 1905-7). It was reprinted by the Buffalo News on November 23, 1998.

William Willett's essay is available online. Some history of Willett from Chapter nine of British Time by de Carle, and the newspaper, The Clare Champion Ltd. Read article.

Sundial story for Detroit from Popular Astronomy, 1901-01. British standard time from Derek Howse, Greenwich time and longitude, Philip Wilson Publishers (1997). Information about Sir Sandford Fleming from The Canadian Encyclopedia Plus (McClelland & Stewart). Details about William Willett from Encyclopaedia Britannica (1911-1927 editions) and internet postings by Doug Spindler and Paul Foxworthy.

Evidence that road fatalities decrease during DST: Broughton J, Sedman RJ. The potential effects on road casualties of double British Summer Time. UK Transport and Road Research Laboratory, research report 228, 1989. Meyerhoff, NJ. The influence of Daylight Saving Time upon motor vehicle fatal traffic accidents. Accident Analysis and Prevention: 10: 207-221, 1978. Joksch HC, Wuerdemann H. The impact of year-round Daylight Saving Time upon traffic deaths and injuries. Center for the environment and Man Inc.; CEM report 4166-506, 1974. British Standard Time and Road Casualties. Transport and Road Research Laboratory, LF213, 1970.

There is occasionally some dispute over the spelling of Sir Sandford Fleming's name. (It is not "Stanford.") Sir Sandford Fleming (1827-1915) is an important figure in Canadian history. Read more about Fleming. There are several schools named after him, including a college in Peterborough, Ontario. Additional information may be found at National Library of Canada and National Research Council Canada. Thanks to A.J. Parl. Thank you to his great great granddaughter Fiona M. MacLean of Louisville, KY who further confirmed the spelling, as her father, brother and nephew are named for him as, John Sandford Fleming MacLean. Thanks also to Ward Cameron for info on Sandford Fleming. Ward is author of "A Natural History and Field Guide to The Canadian Rockies," and several mountain biking books. In the photos with Sandford Fleming, the man holding the hammer is Donald Smith, later Lord Strathcona, who was one of the main financiers of the line. Sandford Fleming is the man standing to his left with the stove pipe hat and the white beard.

For various information about other countries... Thanks to Brett Pickering, Laboratory Supervisor, Palmer Station, Antarctica, for information about Antarctica. Thanks to Stig Hartvig Nielsen regarding Greenland. Thanks to Tulio Fantini regarding Chile. Chilean time inconsistencies from a Copesa article from 10-16 March 1995. New Zealand statistics from various articles, read digest. Palestine from Amos Shapir in the TZ archive. Paraguay law decree no. 16350, dated 2002-02-26. Pakistan experimented with DST for the first time in 2002, ending on 5 Oct 2002 (from Pakistan Herald Publication). Some 80 countries around the world - the vast majority in Europe and North America - already make use of daylight saving time. Asia hardly makes use of daylight saving time. Japan and australia from Leaflet No 27 (pdf) in July 2001 from the National Standards Commission.

Statistics from New South Wales Referendums. Referendum on 1 May 1976. Issue: At present there is a period commonly called 'daylight saving' by which time is advanced by one hour for the period commencing on the last Sunday in October in each year and ending on the first Sunday in March in the following year. Are you in favour of daylight saving ? Returns from 99 electoral districts. RESULTS: Yes 1,882,770 No 868,896 Total Formal 2,751,666 Informal 35,507 Total Votes 2,787,173.

Thank you to Michael Fry for the idea of charting daylight vs. time. Daylight curves from perl module by Ron Hill, as based on code by Paul Schlyter. Note that to preserve bandwidth, the curves are approximate. Near the equator, the curve should have a slight S shape.

Mention of a Private Member's Bill, the British Time (Extra Daylight) Bill of 1995-6 introduced by John Butterfill MP. While this attempt failed, it appeared that the idea that politicians could create extra daylight by legislating for it was unfortunately widespread. From Joseph Myers.

Thanks to Brucie Dolego for help with the spelling and grammar surrounding the phrase "Daylight Saving Time."

Images Images licensed from Corbis, Eyewire, Photodisc. Sir Sanford Fleming photograph adapted from "Driving the last spike of the C.P.R. (Craigallochie, B.C.) 1885." at the National Archives of Canada, C-011371, via the National Library of Canada web site. Australian dam from Hydro Tasmania.
Legal While we have used our best efforts to verify that the information contained herein is accurate, we make no warranties to that effect, and shall not be liable for any damage that may result from errors or omissions in this exhibit.

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