Twice a year the clocks in most of the United States move by an hour, and twice a year a great many people find out about it late. Daylight saving time does not fall on the same calendar date each year; it follows a rule tied to particular Sundays, which is why the dates drift and why an appointment booked across the changeover can quietly slip by sixty minutes.
This article explains exactly when daylight saving time starts and ends in the United States, why the switch is set for 2:00 a.m. local time, why other countries change on entirely different days, and which clocks in your life will update themselves. For the next changeover, see the daylight saving change dates page.
When Does Daylight Saving Time Start and End?
In the United States, daylight saving time begins on the second Sunday in March and ends on the first Sunday in November. Both changes take effect at 2:00 a.m. local time, so clocks jump forward to 3:00 a.m. in spring and fall back to 1:00 a.m. in autumn.
Because the rule names a Sunday rather than a date, the actual day shifts each year within a week or so. The period of daylight saving time therefore runs for about thirty-four weeks, roughly two-thirds of the year, leaving standard time as the shorter season despite its name.
Why the Switch Happens at 2:00 a.m.
Two in the morning was chosen because it disrupts the least. Almost nobody is at work, few trains and flights are moving, and shifting the hour there avoids pushing the change back into the previous calendar day, which would happen if the switch were made at midnight.
The autumn change is the more awkward of the two. When clocks fall back, the hour between 1:00 a.m. and 2:00 a.m. happens twice, so timestamps recorded in local time during that window are genuinely ambiguous. In spring the opposite occurs and that hour simply does not exist, which is why a 2:30 a.m. alarm on the second Sunday in March never rings.
Why Is Daylight Saving Time Not the Same Worldwide?
Each country sets its own rule, so the dates rarely line up. The European Union moves its clocks on the last Sunday in March and the last Sunday in October, several weeks apart from the American change at each end.
That mismatch creates two annual periods, a few weeks long, when the usual gap between American and European cities is an hour narrower or wider than people expect. The southern hemisphere inverts the whole thing, since its summer falls in the northern winter, and a great many countries near the equator never adopted daylight saving time at all because the length of their day barely varies. Treat any remembered offset with suspicion in March, April, October and November.
What Changes on Your Devices?
Anything that knows its own location and connects to a network updates itself. Phones, laptops, tablets and streaming boxes read their offset from a time zone database that already contains the rule, so they change overnight without being asked.
Everything else is manual. Car dashboards, ovens, microwaves, wall clocks, wristwatches and older alarm clocks generally have to be reset by hand, and so do some thermostats and security panels. A useful habit is to check any device that controls something on a schedule, because a heating timer or a store's automatic door lock left an hour out will stay wrong until the next changeover.
Which Places Skip Daylight Saving Time?
Two states opt out entirely. Arizona keeps Mountain Standard Time all year, apart from the Navajo Nation, which does observe the change, and Hawaii stays on Hawaii Standard Time throughout. Most US territories also remain on standard time year-round.
The reasons are climatic and practical rather than contrarian, and they are set out in full in the guide to states that don't observe daylight saving. Indiana is the opposite case: it resisted the change for decades before adopting it statewide in 2006, a saga covered in the article on Indiana time zone history.
The Law Behind the Dates
The current rule is younger than most people assume, and three federal laws shaped it.
- Standard Time Act of 1918: Established legal standard time zones for the United States and introduced a wartime daylight saving scheme that was repealed the following year.
- Uniform Time Act of 1966: Ended a chaotic patchwork of local start and end dates by setting a single national schedule, while allowing an entire state to exempt itself.
- Energy Policy Act of 2005: Extended the season to its present length, moving the start to the second Sunday in March and the end to the first Sunday in November from 2007 onward.
- Sunshine Protection Act proposals: Repeated attempts to make daylight saving time permanent nationwide, none of which has passed both chambers of Congress and become law.
Because Congress can move the boundaries of daylight saving time by statute, the rule has changed several times and could change again. The Department of Transportation, meanwhile, handles the separate question of which zone a county belongs to, so a place can change its offset without any change to the seasonal schedule.
The arguments for and against have barely moved in a century. Supporters point to lighter evenings, lower road casualties and a longer trading afternoon for retail and leisure; opponents point to the disrupted sleep, the measurable rise in accidents in the days after the spring change, and evidence that the energy savings originally claimed are small or absent. Neither side has won outright, which is why the country keeps changing its clocks while debating whether it should.
Getting the Changeover Right
A few precautions cover almost every problem daylight saving time causes.
- When booking across the change, confirm the time in a specific city rather than an abbreviation, since ET means EST in winter and EDT in summer.
- Avoid scheduling anything between 1:00 a.m. and 3:00 a.m. on either changeover night.
- Reset manual clocks the evening before rather than the morning after.
- Re-check recurring international meetings during the weeks when only one side has changed.
The distinction between the year-round label and the seasonal ones is explained in ET vs EST vs EDT, and the live US time board shows which is currently in force.
Conclusion
Daylight saving time in the United States starts on the second Sunday in March and ends on the first Sunday in November, changing at 2:00 a.m. local time in both directions. The rule comes from the Energy Policy Act of 2005, sits on the framework of the Uniform Time Act of 1966, and does not apply in Arizona outside the Navajo Nation or in Hawaii. To see the next change, open the daylight saving dates page or browse the clocks at ustime.now.