Daylight saving time 2024 is coming to an end: When do we “fall back” an hour?

Autumn is here and with it the end of summer time.

Since the passage of the Energy Policy Act of 2005, daylight saving time in the United States begins on the second Sunday in March and ends on the first Sunday in November each year.

When Daylight Saving Time begins in March, the clocks “spring forward” one hour, and when Daylight Saving Time ends in November, the clocks “go back” one hour.

Five questions about the upcoming time change are answered here.

1. When does daylight saving time end in 2024?

This year, Daylight Saving Time ends on Sunday, November 3rd and clocks go back one hour at 2 a.m

With the change, the United States will get darker earlier in the evening.

2. Do we gain or lose an hour of sleep when we “fall back”?

When clocks “reset” at the end of Daylight Saving Time, people gain an hour of sleep.

On Sunday, for example, falling asleep at 10 p.m. will really be like falling asleep at 9 p.m. when the clocks go back an hour at 2 a.m

On the other hand, people lose an hour of sleep when the clocks “spring forward” in March at the start of Daylight Saving Time.

3. What is daylight saving time and why was it introduced?

According to the U.S. Naval Observatory's Division of Astronomical Applications, daylight saving time became law in the United States in 1918 with the passage of the Standard Time Act.

The time change was introduced to maximize daylight hours and thus reduce energy consumption during the First World War.

Over the next few decades, legislatures made unsuccessful attempts to eliminate daylight saving time nationwide, and some individual states and cities reverted to non-daylight saving time hours.

In 1966, Congress passed the Uniform Time Act, which established a uniform daylight saving time across the U.S., according to the U.S. Department of Transportation, the federal agency that oversees time zones.

According to the Uniform Time Act of 1966, states that observe daylight saving time must adhere to federally mandated start and end dates.

States can also “exempt themselves from observing Daylight Saving Time through state law,” according to the DOT.

In 2022, the U.S. Senate unanimously passed a measure, the Sunshine Protection Act, that would have made daylight saving time permanent across the United States. However, the bill was never brought to a vote in the U.S. House of Representatives.

4. In which states do daylight saving time changes not apply?

According to the DOT, Hawaii and Arizona are the only two states in the country that do not participate in Daylight Saving Time, with the exception of the Navajo Nation.

Additionally, five U.S. territories also do not participate in daylight saving time: American Samoa, Guam, Northern Mariana Islands, Puerto Rico and the Virgin Islands.

5. What potential health risks does daylight saving time pose?

Some health experts argue that daylight saving time disrupts the body's natural circadian rhythm.

In 2023, the American Academy of Sleep Medicine formed a coalition to advocate for state and federal legislation that would make standard time permanent throughout the United States. Other organizational members include the National Sleep Foundation, Save Standard Time, the Sleep Research Society and the Society for Research on Biological Rhythms.

According to a study published in the Journal of Clinical Sleep Medicine, the time difference has been linked to more heart attacks, strokes, cardiac arrhythmias, sleep problems, mood disorders and even suicide.

ABC News Medical Contributor Dr. Darien Sutton, recommends that before the clock changes, people gradually change their bedtime to adjust to the change.

Sutton said it's also OK to take a nap if you're feeling tired due to the time change, but try to limit the nap to 30 minutes and take it before 3 p.m

Finally, Sutton said it's important to increase your exposure to sunlight during the day, especially in the morning when the clocks “reset,” and limit your consumption of alcohol and caffeine.

Dr. Avish K. Jain, DO, a physician assistant at Cooper University Hospital and a medical contributor to the ABC News Medical Unit, contributed to this report.