Clocks across much of the United States will fall back once again Sunday as daylight saving time comes to an end.

Congress and some states have tried multiple times this decade to get rid of the twice-yearly exercise but to no avail.

President Donald Trump has expressed support for ending the time changes, arguing that permanent daylight saving time would allow for more daylight to parallel daytime habits while shrinking after-hours activity, including crime. But many health and sleep experts argue against it, citing risks to health and safety.

Here is what to know as we prepare to spin our clocks back Sunday — or let our cellphones do it instantly.

When does daylight saving time end?

Daylight saving time started at 2 a.m. March 8 and ends at 2 a.m. Sunday.

Unlike in the spring, when we lose an hour and the clocks skip the 2 o’clock hour entirely, we will gain an extra hour Sunday, with clocks jumping from 1:59 a.m. back to 1 a.m.

The sun will also start setting earlier across the United States as we head into the late fall and winter.

The extra hour doesn’t necessarily mean more revelry on Halloween night: While some jurisdictions allow bars to serve last call according to Sunday’s updated time, California rules say bars must stop serving alcohol two hours past midnight, regardless of 1 a.m.’s repeat.

How long will standard time last?

Standard time across the United States will remain, as will earlier sunsets and darker evenings, until spring rolls around and daylight saving time starts once again on March 14.

Daylight saving time will end next year on Nov. 7.

The standardized start and end dates have been changed throughout the years, but since 2007, daylight saving time has started the second Sunday in March and ended the first Sunday in November, according to the Astronomical Applications Department of the U.S. Naval Observatory.

Why do we observe daylight saving time?

The practice, established by the Standard Time Act in 1918, according to the Astronomical Applications Department, is an effort to extend the daylight hours we have in the summertime by pushing off sunset an extra hour.

Daylight saving time, a contested idea after it was passed, was quickly repealed in 1919, becoming a local matter. It was re-enacted during the early days of World War II and observed from 1942 to 1945, according to the department.

After the war, the implementation of daylight saving time varied from state to state until the Uniform Time Act was passed in 1966, standardizing the dates of daylight saving time but allowing local exemptions if states or localities didn’t want to participate.

President Richard Nixon briefly moved the nation to year-round daylight saving time in 1974, but the extended morning darkness was widely panned and blamed for incidents of students being struck by vehicles. Congress subsequently reversed his time changes after Nixon resigned later that year.

Which states don’t observe?

Hawaii and most of Arizona don’t observe daylight saving time and therefore don’t change their clocks twice a year, according to the Astronomical Applications Department.

The U.S. territories of American Samoa, Guam, Puerto Rico, the U.S. Virgin Islands and the Northern Mariana Islands also observe permanent standard time, according to the National Conference of State Legislatures.

Do other countries do this?

Most countries observe some version of “summer time,” according to the department, not all of them on the same schedule as the United States.

Most of the countries in the Northern Hemisphere that observe daylight saving time are in Europe and North America.

Some Southern Hemisphere countries also observe some version of daylight saving time, but below the equator, the seasons are swapped, so the start and end dates of their “summer time” are reversed from ours.

According to the Pew Research Center, only about a third of all countries observe daylight saving time. About half of all countries observed it at one point but no longer do.

What recent efforts have been made to end the practice?

Almost all states have considered legislation to stay on standard or daylight saving time, and 19 states have passed bills or resolutions to implement it year-round in the last seven years, according to the National Conference of State Legislatures. But because federal law doesn’t allow for year-round daylight saving time, the states would have to wait for Congress to pass a bill to make the change.

The Senate passed the Sunshine Protection Act in 2022, which would make daylight saving time permanent year-round, but the bill didn’t advance in the House.

A version of the bill introduced in the House in January 2025 stalled in the Senate in summer.

In early October, Trump in a post on Truth Social urged Senate Republicans to “get moving” on the bill, saying the clock changing process “costs our Country a fortune, is bad for Crime, stress on people, Sports, and just about everything else you can imagine.”

What do health experts say?

Some studies suggest that observing daylight saving time year-round could reduce the number of traffic accidents and the amount of crime.

But many health and sleep researchers aren’t in favor of permanent daylight saving time, namely because of the potential hazards of dark mornings, which would mean more children walking or driving to school in the dark.

Sleep experts prefer the back-and-forth of the clocks to permanent daylight saving time, and point to the increased risks of health problems when clocks aren’t closely aligned with the sun.