Daylight saving time is the practice of shifting clocks forward by one hour in spring and back by one hour in fall, moving an hour of daylight from the early morning to the evening during the warmer months. It has stuck around for more than a century largely for bureaucratic reasons rather than logical ones — the original justification for it has mostly fallen apart, but no replacement has won enough political support to actually take its place.
How daylight saving time actually works
In the United States, DST currently begins at 2 a.m. on the second Sunday in March and ends at 2 a.m. on the first Sunday in November, according to the National Institute of Standards and Technology. That means the country spends roughly two-thirds of the year on daylight time and only about a third on standard time, a balance that has shifted more than once since the practice began.
A wartime idea that outlasted the wars
The U.S. first adopted daylight saving time in 1918, during World War I, as a way to conserve fuel and electricity by aligning waking hours more closely with daylight. It was repealed after the war, brought back during World War II, and then fell into a confusing patchwork where cities and states set their own rules, sometimes changing clocks on different dates than their neighbors. That chaos led Congress to pass the Uniform Time Act of 1966, which standardized DST nationwide while still letting states opt out entirely. The Energy Policy Act of 2005 extended the modern DST window by about a month, moving the start earlier into March and the end later into November, in hopes of trimming energy use even further.
Who skips it, and why that’s allowed
Not every part of the country observes daylight saving time. Hawaii and most of Arizona stay on standard time year-round, along with U.S. territories including Puerto Rico, Guam, American Samoa, and the U.S. Virgin Islands. Federal law lets states opt out of DST and stay on standard time permanently, which is exactly what Arizona and Hawaii have done for decades. What states can’t do on their own is the reverse: adopt daylight saving time permanently and skip the twice-yearly switch back to standard time. That would take an act of Congress, which is precisely what a growing number of state legislatures have been pushing for.
Why it persists despite the complaints
Energy conservation was the original case for daylight saving time, but decades of research have found the actual savings are small and inconsistent, with some studies finding little effect on electricity use at all. Meanwhile, evidence has piled up on the downsides: sleep researchers have linked the “spring forward” transition to a measurable, if temporary, increase in heart attacks and traffic accidents in the days immediately following the change. Despite that mixed record, daylight saving time has hung on mainly through inertia — no single alternative has won enough political consensus to replace it, even though bills like the Sunshine Protection Act, which would make daylight saving time permanent nationwide, have repeatedly been introduced in Congress.
Momentum for change has been building anyway. By 2025, roughly two dozen states had passed legislation supporting a permanent switch to either daylight saving or standard time, contingent on Congress changing federal law to allow it. The Sunshine Protection Act has passed one chamber of Congress in recent sessions but has yet to become law, leaving the country’s clocks exactly where they’ve been for years: springing forward, falling back, and reigniting the same debate every six months.