Daylight saving time in the United States

Most of the United States observes daylight saving time, the practice of setting the clock forward by one hour when there is longer daylight during the day, so that evenings have more daylight and mornings have less. Exceptions include Arizona, Hawaii, and the territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the United States Virgin Islands. The Uniform Time Act of 1966 established a uniform set of rules for states opting to observe daylight saving time.
In the US, 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, 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 every year, about 65% of the entire year.
Federal law supports states that opt to switch between standard time and daylight saving time, despite some unsuccessful efforts to do away with this practice. In 2022, the United States Senate passed the Sunshine Protection Act which would have permanently activated daylight saving time, but it did not become law, because it was not approved by the US House of Representatives.
The following table lists recent-past and near-future starting and ending dates of daylight saving time in the United States:

Year	Start	End




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History of DST in the United States

proposed a form of daylight time in 1784. Writing as an anonymous "subscriber", his tongue-in-cheek essay "An Economical Project for Diminishing the Cost of Light", written to the editor of The Journal of Paris, observed that Parisians could save on candles by getting out of bed earlier in the morning, making use of the natural morning light instead. By his calculations, the total savings by the citizens of Paris would be the approximate equivalent of $200 million today. Franklin's suggestion seems to have been more of a joke than a real proposal, and nothing came of it.

1916–1966: Early, inconsistent use

During World War I, in an effort to conserve fuel, Germany began observing DST on May 1, 1916, and 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 confirmed the existing standard time zone system and set summer DST to begin on March 31, 1918. The idea was unpopular, especially with farmers because DST meant they had less time in the morning to get their milk and harvested crops to market. Congress abolished DST after the war, overriding President Woodrow Wilson's veto. DST became a local option. New York City continued to observe a metropolitan DST, while rural areas outside the city did not. Because of NYC's position as a financial capital, other places followed. A nationwide DST would not be established again until World War II. On February 9, 1942, President Franklin Roosevelt instituted year-round DST, called "War Time". It lasted until the last Sunday in September 1945. After 1945, many states and cities east of the Mississippi River adopted summer DST.
From 1945 to 1966, there was no federal law on daylight saving time, so localities could choose when it began and ended or drop it entirely. A complicated patchwork of daylight saving policies that varied in length and by city, state, and municipality emerged. As of 1954, only California and Nevada had state-wide DST west of the Mississippi, and only a few cities between Nevada and St. Louis. In the 1964 Official Railway Guide, 21 of the 48 contiguous states had no DST anywhere. By 1965, there were 18 states that observed daylight saving for six months each year, eighteen states that did not have formal policies but held cities or towns with their own daylight saving standards and another 12 states that did not implement daylight saving at all. Meanwhile, portions of North Dakota and Texas observed a sort of "reverse" daylight saving time, essentially setting their clocks back an hour rather than moving them forward.

1967–1972: Federal standard established

By 1962, the transportation industry found the lack of consistency confusing enough to push for federal regulation. The result was the Uniform Time Act of 1966, signed by President Lyndon Johnson on April 14. Beginning in 1967, the act mandated standard time within the established time zones and provided for advanced time: Clocks would be advanced one hour beginning at 2:00 a.m. on the last Sunday in April and turned back one hour at 2:00 a.m. on the last Sunday in October. States were allowed to exempt themselves from DST as long as the entire state did so. If a state chose to observe DST, the time changes were required to begin and end on the established dates. The act also required states that used daylight saving time in 1966 to follow the same schedule. The newly created Department of Transportation was given power to enforce the law.
In 1967, Arizona and Michigan became the first states to exempt themselves from DST. In 1972, the act was amended, allowing those states split between time zones to exempt either the entire state or that part of the state lying within a different time zone.
, the following states and territories do not observe DST: Arizona, Hawaii, American Samoa, Guam, The Northern Mariana Islands, Puerto Rico, and the Virgin Islands.

1973–1975: Year-round experiment

During the 1973 oil embargo by the Organization of Arab Petroleum Exporting Countries, in an effort to conserve fuel, Congress enacted a trial period of year-round DST, beginning January 6, 1974, and ending April 27, 1975. The trial was hotly debated. Those in favor pointed to increased daylight hours in the winter evening: more time for recreation, reduced lighting and heating demands, reduced crime, and reduced automobile accidents. The opposition was concerned about children leaving for school in the dark and the construction industry was concerned about morning accidents. After several morning traffic accidents involving schoolchildren in Florida, including eight children who were killed, Governor Reubin Askew asked for the year-round law to be repealed.
Over three months from December to March, public support dropped from 79% to 42%. Some schools moved their start times later. Shortly after the end of the Watergate scandal caused a change of administration, the act was amended in October 1974 to return to standard time for four months, beginning October 27, 1974, and ending February 23, 1975, when DST resumed. When the trial ended in October 1975, the country returned to observing summer DST.

1975–1986: Extension of daylight saving time

The DOT, evaluating the plan of extending DST into March, reported in 1975 that "modest overall benefits might be realized by a shift from the historic six-month DST in areas of energy conservation, overall traffic safety and reduced violent crime." However, DOT also reported that these benefits were minimal and difficult to distinguish from seasonal variations and fluctuations in energy prices.
Congress then asked the National Bureau of Standards to evaluate the DOT report. Its report, "Review and Technical Evaluation of the DOT Daylight Saving Time Study", found no significant energy savings or differences in traffic fatalities. It did find statistically significant evidence of increased fatalities among school-age children in the mornings during the four-month period January–April 1974 as compared with the same period of 1973. NBS stated that it was impossible to determine how much, if any, of this increase was due to DST. When these data were compared between 1973 and 1974 for the months of March and April, no significant difference was found in fatalities among school-age children in the mornings.
In 1986, Congress enacted P.L. 99-359, amending the Uniform Time Act by changing the beginning of DST from last Sunday in April to the first Sunday in April and having the end remain the last Sunday in October. These start and end dates were in effect from 1987 to 2006. The time was adjusted at 2:00 a.m. local time.

2005–2009: Second extension

By the Energy Policy Act of 2005, daylight saving time was extended in the United States beginning in 2007. From that year, DST begins on the second Sunday of March and ends on the first Sunday of November. In years when April 1 falls on Monday through Wednesday, these changes result in a DST period that is five weeks longer; in all other years the DST period is four weeks longer.
Under Section 110 of the act, the US Department of Energy was required to study the impact of the 2007 DST extension no later than nine months after the change took effect. The report, released in October 2008, reported nationwide electricity savings of 0.03% for the year 2007.
An October 2008 study conducted by the University of California at Santa Barbara for the National Bureau of Economic Research found that the 2006 DST adoption in Indiana increased energy consumption in Indiana by an average of 1%. Although consumption for lighting dropped by 4.5% as a result of the DST adoption, consumption for heating and cooling increased 2% to 10%. The cost to the average Indiana household of the DST adoption was determined to be $3.29 per year, for an aggregate cost of $1.7 million to $5.5 million per year.
The United States Chamber of Commerce has praised the extension of daylight saving under the 2005 law, which increased the amount of shopping and commerce after work in the evenings. In the golf industry, the group has noted an exceptional increase in revenue of "$200 million in additional sales of golf clubs and greens fees". The extension of daylight saving has also had a notable impact on Halloween and candy sales. Wyoming senator Michael Enzi and Michigan representative Fred Upton advocated the extension from October into November especially to allow children to go trick-or-treating in more daylight. In some areas, the extension of daylight saving time in March and November has pushed back sunrise to as late as 8:30 a.m.