Daylight Saving Time

Daylight saving time in most of the United States begins at 2:00 a.m. local time on the second Sunday in March and ends at 2:00 a.m. local daylight time on the first Sunday in November. The March clock jumps forward to 3:00 a.m.; the November clock moves back to 1:00 a.m.

The current date rule has applied since 2007. It does not cover every US location: Hawaii, most of Arizona and several territories stay on standard time throughout the year. Daylight saving time changes the legal clock, not the amount of sunlight.

How the Current Clock-Change Rule Works

The start date is the second Sunday in March. At 1:59:59 a.m. standard time, the next displayed second is 3:00:00 a.m. daylight time. The local date is 23 hours long because the hour beginning at 2:00 does not occur.

The end date is the first Sunday in November. At 1:59:59 a.m. daylight time, clocks return to 1:00:00 a.m. standard time. The hour from 1:00 through 1:59 occurs twice, making a 25-hour local date.

This is why a time-zone abbreviation matters around the fall transition. “1:30 a.m. Eastern time” can identify two different instants on that Sunday. “1:30 a.m. EDT” means the first occurrence, while “1:30 a.m. EST” means the second. Airline, medical and computer systems often use offsets from Coordinated Universal Time to remove the ambiguity.

The table below calculates both transition dates for each year. For 2026, daylight saving time runs from March 8 through November 1. The 2026 calendar also places both clock changes alongside holidays, moon phases and seasons.

What Daylight Saving Time Actually Changes

Moving the clock forward does not create daylight. Earth’s rotation and orbit determine sunrise and sunset. DST shifts the clock labels attached to those events, producing a later clock-time sunset and a later clock-time sunrise.

Suppose sunrise and sunset under standard time would be 5:30 a.m. and 6:30 p.m. Advancing the legal clock changes those labels to 6:30 a.m. and 7:30 p.m. People following the same clock schedule experience more light after work or school and less in the early morning.

The effect depends on latitude, season and daily routine. Locations near the equator have less seasonal variation to rearrange. Farther north, summer days are already long and winter days remain short regardless of the clock. The US time-zones guide explains the difference between a zone’s standard and daylight abbreviations.

The official term is daylight saving time, not daylight savings time. “Saving” describes the practice of shifting usable daylight to a later clock hour; it is not a bank account of daylight being saved.

US Daylight Saving Time History

The federal government first introduced daylight saving time in 1918 through the Standard Time Act during World War I. The same legislation formalized national standard-time zones. The daylight provision was unpopular in many rural communities, and Congress repealed the nationwide requirement in 1919 while allowing local use to continue.

During World War II, year-round advanced time returned nationally. The 1942 measure became known as “War Time” and lasted until 1945. Afterward, states and cities again adopted different rules. A trip or broadcast could cross places changing clocks on different dates—or not changing them at all.

The Uniform Time Act of 1966 addressed that patchwork. It established national start and end dates for places choosing to observe DST, while allowing a state to exempt itself. Congress amended the law in 1972 so a state split between time zones could exempt the part in one zone.

The rules have changed several times:

Period	General federal schedule
1967-1973	Last Sunday in April to last Sunday in October
1974	Temporary year-round experiment began January 6 during the energy crisis
1975-1986	Seasonal schedule restored, generally last Sunday in April to last Sunday in October
1987-2006	First Sunday in April to last Sunday in October
2007-present	Second Sunday in March to first Sunday in November

The 1974 experiment was shortened after concerns that included dark winter mornings. Congress restored standard time for part of the winter before the original trial would have ended.

Why the Rule Changed in 2007

The Energy Policy Act of 2005 extended DST beginning in 2007. The spring start moved three or four weeks earlier, from the first Sunday in April to the second Sunday in March. The autumn end moved one week later, from the last Sunday in October to the first Sunday in November.

Congress required the Department of Energy to study the energy effect. Its report estimated that the extension reduced total US electricity consumption by about 0.03 percent during the study period and total primary energy consumption by roughly 0.02 percent. Those are small national changes, not proof that every household or region saves energy.

Energy use has changed since the original DST arguments emphasized evening lighting. Air conditioning, heating, work patterns, commercial schedules and efficient lighting complicate the balance. Supporters also point to recreation and commerce after work; critics emphasize dark mornings, sleep disruption and schedule costs.

Federal law retains the current schedule unless Congress changes it. Bills proposing year-round daylight time or other revisions do not change clocks merely by being introduced or passing one chamber.

Where Daylight Saving Time Is Not Observed

Hawaii stays on Hawaii Standard Time throughout the year. Its tropical latitude means seasonal daylight varies less than in much of the mainland, reducing the practical case for a seasonal shift.

Most of Arizona remains on Mountain Standard Time. During summer, that gives most of the state the same clock time as Pacific Daylight Time in neighboring California and Nevada. The Navajo Nation observes DST across its multistate territory, including its portion of Arizona, so travelers within the state can still encounter a clock boundary.

American Samoa, Guam, the Northern Mariana Islands, Puerto Rico and the US Virgin Islands also do not observe DST. The Aleutian Islands are different from Hawaii even though both are in the Hawaii-Aleutian zone: the Aleutians observe the seasonal change while Hawaii does not.

Under the Uniform Time Act, a state may choose standard time year-round. If it observes DST, it must follow the federally mandated dates. Current law does not let a state independently choose daylight time year-round. That distinction explains why some enacted state measures are conditional on congressional action.

How to Prepare for the Time Change

Phones and networked computers usually update automatically when their operating systems have current time-zone data. Appliances, vehicle clocks, mechanical watches and older electronic clocks may still require manual changes. Some devices manufactured for pre-2007 rules can switch on the old April or October dates.

A useful check before the transition includes:

• Confirm the time zone and automatic-time setting on travel devices.
• Change manual clocks before bed if you do not need exact 2:00 a.m. timing.
• Verify alarms, medication reminders and timed household equipment.
• Use the time-zone abbreviation or UTC offset for events during the repeated fall hour.
• Check schedules directly when traveling through an area that does not observe DST.

Smoke-alarm campaigns often use the clock change as a reminder to test alarms, but replacement schedules depend on the manufacturer and local fire guidance. The time change itself does not determine whether a battery or alarm must be replaced.

DST, Seasons and Calendar Dates

Daylight saving time is not tied to an equinox. The March equinox and September equinox are astronomical events whose dates and times vary slightly; the clock changes are Sunday rules created by law. The March transition normally occurs before the spring equinox, and the November return occurs well after the autumn equinox.

The relationship also differs by hemisphere. Countries in the Southern Hemisphere that use summer time generally advance clocks during the northern autumn and return during the northern spring. Other countries use different dates or no seasonal change at all.

For a date calculation involving a transition, specify both place and time zone. Counting calendar days with the days-between-dates calculator is straightforward, but elapsed hours across a spring or fall clock change may be one hour shorter or longer than the number of dates suggests.