Daylight saving time in the United States

Daylight saving time in the United States is the practice of setting the clock forward by one hour during the warmer part of the year, so that evenings have more daylight and mornings have less. Most areas of the United States observe daylight saving time (DST), the exceptions being Arizona (except for the Navajo, who do observe daylight saving time on tribal lands),Hawaii, and the overseas territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands.

Daylight saving time starts on the second Sunday in March and ends on the first Sunday in November, with the time changes taking place at 2:00 a.m. local time. With a mnemonic word play referring to seasons, clocks "spring forward and fall back"—that is, in springtime the clocks are moved forward from 2:00 a.m. to 3:00 a.m., and in fall they are moved back from 2:00 a.m. to 1:00 a.m. Daylight saving time lasts for a total of 34 weeks (238 days) every year, about 65% of the entire year (even in leap years).

The following table lists recent past and near future starting and ending dates of daylight saving time in the United States:

During World War I, in an effort to conserve fuel, Germany began observing DST on May 1, 1916. The rest of Europe soon followed. The plan was not adopted in the United States until the Standard Time Act of March 19, 1918, which established standard time zones and set summer DST to begin on March 31, 1918 (reverting October 27). The idea was unpopular and Congress abolished DST after the war, overriding President Woodrow Wilson's veto. DST became a local option and was observed in some states until World War II, when President Franklin Roosevelt instituted year-round DST, called "War Time", on February 9, 1942. It lasted until the last Sunday in September 1945. After 1945 many states and cities east of the Mississippi River (and mostly north of the Ohio and Potomac Rivers) adopted summer DST.

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