A history of daylight saving time in the United States

Daylight saving time in the United States is set in federal law and has changed several times, according to the U.S. Naval Observatory and the National Institute of Standards and Technology. The U.S. Naval Observatory says Congress first put daylight saving time into law in 1918, then revised it in later statutes, most recently with dates that have applied since 2007. NIST adds that daylight saving time and time zones are regulated by the U.S. Department of Transportation.

Before federal law and the 1918 act

The U.S. Naval Observatory reports that railroads instituted standard time in time zones in 1883 in the United States and Canada. It says Congress did not put this into U.S. law until the Standard Time Act passed on March 19, 1918. NIST states that “daylight saving time, or DST, is the period of the year when clocks are moved one hour ahead,” and that it was formally introduced in the United States in 1918.

Repeal and local control after World War I

The U.S. Naval Observatory says the Standard Time Act also established daylight saving time and that the idea was contentious. According to the U.S. Naval Observatory, daylight saving time was repealed in 1919, while standard time in time zones remained in law. The U.S. Naval Observatory states that daylight time then became a local matter.

World War II national observance and postwar variation

The U.S. Naval Observatory states that daylight saving time was re-established nationally early in World War II. It reports that it was continuously observed from Feb. 9, 1942, to Sept. 30, 1945. After the war, the U.S. Naval Observatory says states and local governments used it in different ways.

The Uniform Time Act of 1966

According to the U.S. Naval Observatory, the Uniform Time Act of 1966 created uniform nationwide start and end dates for daylight saving time in the United States. The U.S. Naval Observatory says it allowed for local exemptions from its observance. The U.S. Naval Observatory states that the law set the switch to the last Sunday in April for the start and the last Sunday in October for the end, with the shift at 2 a.m. local time.

Changes during the 1970s and 1980s

The U.S. Naval Observatory reports that during the energy crisis years, Congress enacted earlier starting dates. It says that in 1974 daylight saving time began on Jan. 6, and in 1975 it began on Feb. 23. After those two years, the U.S. Naval Observatory notes, the starting date reverted to the last Sunday in April. The U.S. Naval Observatory states that in 1986 a law shifted the starting date to the first Sunday in April, beginning in 1987, while the ending date remained the last Sunday in October.

The Energy Policy Act of 2005 and the 2007 rules

The U.S. Naval Observatory says the Energy Policy Act of 2005 revised the start and end dates for daylight saving time. Beginning in 2007, the U.S. Naval Observatory says the period runs from the second Sunday in March to the first Sunday in November, with 2 a.m. local time clock changes. NIST states that these changes extended the length of daylight saving time and that Congress retained the right to revert to the prior law.

How agencies describe today’s framework

NIST explains that daylight saving time moves one hour of daylight from the morning to the evening during the period when clocks are advanced. It states that most of the United States and its territories observe daylight saving time, with noted exceptions including Hawaii and most of Arizona. NIST also notes that while it distributes official time, the U.S. Department of Transportation regulates daylight saving time and time zones.