Why Do We Have Daylight Saving Time?

What does daylight saving time actually do?

Daylight saving time (DST) is the part of the year when clocks are set one hour ahead of standard time.^[1] Clocks go forward an hour when DST begins and back an hour when it ends, a pattern summed up as "spring forward, fall back."^[1] The switch moves one hour of daylight from the morning to the evening.^[1]

In the United States, this gives more sunlit hours in the evening during the warmest months.^[1] Supporters hope it puts sunlight into more of the hours when people are usually active.^[6] About one-third of countries observe DST, many of them in Europe and North America, according to a 2023 analysis cited by the Congressional Research Service (CRS).^[6]

When did daylight saving time start?

The idea was considered worldwide for years before any country adopted it.^[4] Imperial Germany was the first: on April 6, 1916, its Federal Council ordered a change in the clocks for the months of May through September.^[4] The aim was to conserve fuel during World War I, and as the war went on, the rest of Europe gradually followed.^[6]

The United States followed with the Standard Time Act of March 19, 1918, which put time zones into federal law and also established DST.^[3] The clock change was contentious, and Congress repealed it in 1919, overriding a veto by President Woodrow Wilson.^[3][6]

DST returned nationally in World War II as year-round "War Time," observed continuously from February 9, 1942, to September 30, 1945.^[3][6] After the war its use varied among states and localities, until the Uniform Time Act of 1966 standardized the start and end dates.^[3] During the 1973 oil embargo, Congress began a trial of year-round DST on January 6, 1974, then restored four months of standard time from October 27, 1974.^[6]

How does daylight saving time work in the United States today?

The Uniform Time Act of 1966 still governs DST across the country.^[2] The current dates were set by the Energy Policy Act of 2005 and have applied since 2007: DST begins on the second Sunday in March and ends on the first Sunday in November.^[3] In 2026, DST runs from March 8 to November 1.^[1] The 2005 law lengthened DST by about one month, to 238 days, or about 65% of the year.^[1]

The U.S. Department of Transportation (DOT) oversees the country's time zones and the uniform observance of DST, because time standards are important to many forms of transportation.^[2] DOT has no power to repeal or change DST, however; only Congress can change the period when it is observed.^[2][6]

A state may exempt itself from DST by passing a state law, but states do not have the authority to stay on DST all year.^[2] DST is not observed in Hawaii, most of Arizona, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands.^[6] Hawaii exempted itself in 1967 and Arizona in 1968, though residents of the Navajo Nation, which spans part of Arizona, observe DST.^[6]

Does daylight saving time save energy?

Saving energy was the reason for lengthening DST under the 2005 law, but official studies have found only small effects.^[1][5][6] The Department of Energy (DOE) examined the four weeks of DST added in 2007 in a report to Congress dated October 2008.^[5] It found that the extra weeks saved about 1.3 terawatt-hours of electricity, an average of 0.48 percent for each day of extended DST.^[5] That was 0.03 percent of the country's electricity use over the year, and roughly 0.02 percent of total U.S. energy consumption in 2007.^[5]

The savings came over three to five hours in the evening and were slightly offset by higher use in the morning.^[5] Changes in traffic volume and gasoline use were statistically insignificant.^[5] Savings also differed by region: the daily figure was lowest in the Mid-South regions and highest in California.^[5]

• Mid-South regions0.27%
• National average0.48%
• California0.93%

Source: U.S. Department of Energy [5]

A DOT report in 1975 concluded that the possible benefits of a longer DST were small and difficult to isolate from seasonal patterns and changes in energy supply and prices.^[6] A later review by the National Bureau of Standards found no significant energy savings.^[6] CRS also notes at least one study, based in Indiana, which found that DST increased electricity demand.^[6]

Will the United States make one time permanent?

Nineteen states have passed laws to adopt permanent DST, but these can take effect only if Congress allows it.^[6] In Congress, a bill called the Sunshine Protection Act would make DST permanent in most of the country.^[6] Versions have been introduced since 2018, and the Senate passed one in March 2022, but the House took no further action on it.^[6]

On July 14, 2026, the House passed the current version, H.R. 139.^[6] As of October 2, 2026, the Senate had recessed without bringing the bill to a vote, and senators were not due back until after the midterm elections on November 3.^[8] Under the current rules, DST still ends on November 1, 2026.^[1]

Supporters say permanent DST would provide more daylight at the times when Americans are most active.^[8] Opponents say it would bring darker and potentially more hazardous winter mornings, with children waiting for school buses and parents driving to work in darkness.^[8] Several scientific and medical organizations, including the American Academy of Sleep Medicine, support permanent standard time instead.^[6] Another bill, H.R. 9638, would repeal DST and keep standard time all year.^[6]

What are the European Union's rules on changing the clocks?

Since 2001, an EU directive has required all member states to switch to summer time on the last Sunday of March and back to standard time on the last Sunday of October.^[7] On September 12, 2018, the European Commission proposed ending the seasonal changes.^[7] Its public consultation drew around 4.6 million replies, 84% of them in favor of ending the changes.^[7] The European Parliament backed the proposal on March 26, 2019, but the Council of the European Union has not finalized its position, so the EU still changes its clocks twice a year.^[7][6]