It’s time to fall back again.

On Sunday morning the clock strikes 01:00 twice, because summer time is coming to an end again.

Here’s what you need to know about daylight saving time and why the US changes its clocks twice a year.

When does daylight saving time end?

Daylight saving time started on March 10 and ends on November 3.

Unlike in the spring, when we lose an hour and the clocks skip the 2 o’clock hour altogether, on Sunday we gain an extra hour, with the clocks jumping back from 1:59 a.m. to 1:00 a.m.

The sun will also set earlier in the US as temperatures continue to cool and we enter the late fall and winter months.

Why does this happen?

The practice, which was introduced in 1918 by the Standard Time Act, is an attempt to extend the daylight hours we have in the summer by delaying sunset by an hour, according to the U.S. Astronomical Applications Department.

Daylight saving time, a controversial idea after it was first adopted, was quickly abolished in 1919 and became a local matter. According to the department, it was reenacted during the early days of World War II and observed between 1942 and 1945.

After the war, implementation of daylight saving time varied from state to state until the 1966 passage of the Uniform Time Act, which standardized the dates of daylight saving time but allowed local exceptions if states or localities did not want to participate.

According to the department, the standardized start and end dates have changed over the years, but since 2007, daylight saving time begins on the second Sunday in March and ends on the first Sunday in November.

How long is standard time?

Standard time in the US will remain in effect, along with earlier sunsets and dark evenings, until spring arrives and daylight saving time begins again.

In 2025, daylight saving time starts on Sunday, March 9 and ends on Sunday, November 2, when it’s time to repeat the process.

Are there states that do not comply with this?

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

Is the US the only country doing this?

No, according to the department, most countries use some version of ‘summer time’. In the Northern Hemisphere, most countries that observe daylight saving time are in Europe and North America.

Although other countries practice some version of daylight saving time, not all do so on the same schedule as the US

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

According to the Pew Research Center, only about a third of all countries practice daylight saving time. At one point, about half of all countries observed the practice, but no longer do so.

What efforts have been made to put an end to this practice?

In March 2022, the U.S. Senate passed the Sunshine Protection Act, which would make daylight saving time permanent year-round and usher in the era of changing our clocks.

Under the bill, Hawaii and most of Arizona would continue to observe standard time year-round.

But the bill has since been stalled in the House of Representatives, meaning the US will continue to observe the time change until it is passed in that chamber and then signed by the sitting president.

Nearly all states have considered legislation to enforce standard or daylight saving time, and 20 states have passed bills or resolutions in the past six years to implement year-round daylight saving time, according to the National Conference of State Legislatures. But because federal law does not currently allow daylight saving time year-round, states would have to wait until Congress passes the bill to make the change.

What do health experts say?

Some research suggests that using daylight saving time year-round could reduce the number of traffic accidents and the amount of crime.

But a number of experts are not in favor of permanent daylight saving time. That’s because, according to sleep experts, the sun should reach its highest point in the sky around noon, which is known as solar time.

During Standard Time, people in the Central Time Zone in the US are perfectly aligned with solar time, but during Daylight Savings Time they move further away from that clock.

The more mismatch with solar time, the greater the risk of health problems, Dr. Karin Johnson, professor of neurology at UMass Chan Medical School-Baystate and board member of Save Standard Time, a nonprofit that advocates for permanent standard time. NBC News in 2022.

Sleep experts prefer clock back and forth over permanent daylight saving time. When people wake up in the dark, hormones such as cortisol may be higher, which can make people feel sleepier, Dr. Kin Yuen, a sleep medicine specialist at the University of California, San Francisco, and a fellow at the American Academy of Sleep Medicine, said in 2022.

Because the sun shines later, people may go to sleep later during daylight saving time, which can slow the body’s production of melatonin.

Additionally, a June 2022 study found that people whose clock times did not closely match the sun had 22% more traffic fatalities than those who lived within 30 minutes of solar time.