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Daylight Saving Time in the US: How It Works and Who Skips It

Twice a year, most of the US shifts its clocks by an hour. Here is how the system actually works and why a couple of states sit it out.

Clocks move forward in March, back in November

Daylight saving time begins on the second Sunday in March, when clocks move forward one hour (commonly remembered as "spring forward"), and ends on the first Sunday in November, when clocks move back one hour ("fall back").

The Uniform Time Act of 1966 standardized the dates

Before 1966, states and even individual cities could set their own daylight saving schedules, creating a confusing patchwork. The federal Uniform Time Act established uniform start and end dates nationwide, though it still allows states to opt out of observing daylight saving time entirely.

Arizona and Hawaii do not observe daylight saving time

Most of Arizona (apart from the Navajo Nation, which does observe it) and Hawaii stay on standard time year-round, opting out under the flexibility the Uniform Time Act provides to individual states.

The original rationale was energy savings

Daylight saving time was first adopted nationally during World War I, modeled on similar European wartime measures intended to reduce energy use by shifting daylight hours later into the evening; that first federal version was repealed within a year after backlash, notably from farmers.

There is an active push toward making DST permanent

Multiple states have passed legislation that would adopt permanent daylight saving time if Congress allows it, and federal legislation on the topic has been introduced in recent sessions of Congress, though switching to permanent DST nationwide requires federal action, not just state law.

The time change is linked to short-term sleep disruption

Losing an hour in March in particular is associated with a temporary increase in sleep disruption and, in some studies, other short-term effects, which is part of why the shift to permanent time (in either direction) has drawn public health interest.

Not every country follows the same schedule

Many countries observe some form of daylight saving time, but the exact start and end dates vary by region and are not synchronized with the US schedule, which is why the time difference between the US and other countries can shift by an hour for part of the year and then shift back.

Why the debate is "permanent standard time" vs. "permanent daylight time," not just for or against DST

Much of the current policy debate is not simply whether to keep changing clocks, but which single time to lock in if the twice-yearly change is eliminated β€” permanent standard time (darker evenings, lighter mornings) versus permanent daylight time (lighter evenings, darker mornings) β€” and health and safety researchers are not unanimous on which is preferable.

Frequently Asked Questions

Do US territories like Puerto Rico observe daylight saving time?

No. Puerto Rico, along with several other US territories including American Samoa, Guam, the Northern Mariana Islands, and the US Virgin Islands, does not observe daylight saving time, similar to Arizona and Hawaii.

Has the US ever tried permanent daylight saving time before?

Yes, briefly β€” the US adopted year-round daylight saving time in 1974 during an energy crisis, but it proved unpopular, particularly due to darker winter mornings, and Congress reverted to the seasonal schedule before the trial period even finished.

Will daylight saving time definitely become permanent soon?

It is uncertain β€” while some federal legislation on the topic has advanced further than in past years, and multiple states have pre-emptively passed conditional laws, any nationwide switch to permanent daylight time requires an act of Congress, so checking current legislative status is the only way to know for sure.