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Daylight Saving Time
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Illustration showing clocks for daylight saving time changes in the Northern Hemisphere. Large clocks show spring forward and fall back, with smaller clocks for Greenland, Cuba, and Europe.
Daylight Saving Time?
Daylight Saving Time Map of the United States color-coded by earliest sunrise times under daylight saving scenarios, with time zone boundaries and interactive controls on the left. Cook County, Illinois sunrise and sunset details shown at bottom.
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Illustration showing clocks for daylight saving time changes in the Northern Hemisphere. Large clocks show spring forward and fall back, with smaller clocks for Greenland, Cuba, and Europe.
Daylight Saving Time An illustration of Daylight Saving Time as it is practiced around the world.

Daylight Saving Time

timekeeping
Also known as: summer time
Written by
Jonathan D. Betts
Curator of Horology, Royal Observatory Greenwich, National Maritime Museum.
Jonathan D. Betts
Fact-checked by
Britannica Editors
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree....
Britannica Editors
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•History

Daylight Saving Time, system for uniformly advancing clocks, so as to extend daylight hours during conventional waking time in the summer months. In countries in the Northern Hemisphere, clocks are usually set ahead one hour in late March or in April and are set back one hour in late October or November. The practice was first suggested in a whimsical essay by Benjamin Franklin in 1784. In 1907 an Englishman, William Willett, campaigned for setting...

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