Come Sunday, March 9, most of America will "spring forward" for daylight saving time, which means more sunlight in the evenings, and later sunsets.
It also means clocks will turn ahead by one hour -- and people will get less sleep in the process.
In the U.S., daylight saving time lasts for a total of 34 weeks, typically running from early-to-mid March to the beginning of November in states that observe it. The clocks were last changed Nov. 3, at the end of daylight saving in 2024, when they "fell back" one hour.
As the time change approaches, here's what to know about daylight saving time, how springing forward could affect your sleep and more.
On daylight saving time, do we lose an hour of sleep or gain an hour?
When daylight saving time begins in March each year, clocks "spring forward," which leads to later sunsets. It also means you'll lose an hour of sleep.
For 2025, daylight saving time takes place at 2 a.m. Sunday, March 9. Most clocks will automatically set one hour ahead at that time, though some may have to be changed manually, like freestanding clocks or those on certain appliances.
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When daylight saving time comes to an end for 2025 on Nov. 2, the clocks will "fall back," which means you'll gain an hour of sleep.
How daylight saving time impacts sleep
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The brain has a master clock that is set by exposure to sunlight and darkness. This circadian rhythm is a roughly 24-hour cycle that determines when we become sleepy and when we’re more alert. The patterns change with age, one reason that early-to-rise youngsters evolve into hard-to-wake teens.
Morning light resets the rhythm. By evening, levels of a hormone called melatonin begin to surge, triggering drowsiness. Too much light in the evening — that extra hour from daylight saving time — delays that surge and the cycle gets out of sync.
Sleep deprivation is linked to heart disease, cognitive decline, obesity and numerous other problems. And that circadian clock affects more than sleep, also influencing things like heart rate, blood pressure, stress hormones and metabolism.
The American Academy of Sleep Medicine, based in Illinois, has called on policymakers to abolish seasonal time changes and instead adopt permanent standard time, which, according to the organization, "follows science and prioritizes public health, safety, and efficiency."
“The switch to daylight saving time in the spring may seem harmless, but the reality is far more complicated,” Jay Pea, co-chair of the coalition and president of Save Standard Time, said in an article from the AASM. "It disrupts our body clocks, affects our sleep quality, and increases the risk of avoidable health and safety incidents, such as motor vehicle accidents, cardiovascular events, and even workplace errors in the days following the time change. Adopting permanent standard time, on the other hand, offers a better solution for year-round well-being.”
What's the difference between standard time and daylight saving time?
As it stands, Illinois shifts between the two. "Spring forward" is when the state enters daylight saving time, and the "fall back" marks a return to standard time.
According to the website Time and Date, standard time is the local time in a country or region when daylight saving time is not in use.
"More than 60% of the countries in the world use standard time all year," the site says. "The remaining countries use DST during the summer months, generally setting clocks forward one hour from standard time."
According to the AASM, standard time "aligns more closely with our body's natural circadian rhythms."
"It offers more sunlight in the morning, helping people wake up and feel more alert, while the evenings gradually become dark earlier, signaling to our bodies that it’s time to wind down," the AASM said. "This natural alignment supports more restful and consistent sleep."
When daylight saving time is in effect, however, evening light exposure is prolonged, the AASM says, "which can delay bedtime and disrupt sleep patterns."
"The increased morning darkness, particularly in winter if daylight saving time were permanent, would create additional challenges, such as unsafe conditions for commuters and children heading to school," the article stated.
Why was daylight saving time created?
Daylight savings time was first instated in the U.S. more than a century ago, though some people credit its invention to an essay written by Benjamin Franklin in 1784.
In an essay about saving candles, Franklin wrote "Early to bed, early to rise makes a man healthy, wealthy and wise." But that was meant more as satire than a serious consideration.
Germany was the first to adopt daylight saving time on May 1, 1916, during World War I as a way to conserve fuel. The rest of Europe followed soon after.
Two years later, the U.S. adopted daylight saving time in March of 1918, with the intention of adding additional daylight hours also as a way to help save energy costs during World War I, according to the U.S. Department of Defense. However, it was unpopular and abolished after World War I.
On Feb. 9, 1942, Franklin Roosevelt instituted a year-round daylight saving time, which he called "wartime." The law, was again meant to instate daylight saving time to "help conserve fuel and promote national security defense," the department said. This lasted until Sept. 30, 1945.
Daylight saving time didn't become standard in the U.S. until the passage of the Uniform Time Act of 1966, which mandated standard time across the country within established time zones. It stated that clocks would advance one hour at 2 a.m. on the last Sunday in April and turn back one hour at 2 a.m. on the last Sunday in October.
The standard schedule for daylight saving changed in 2005, thanks in part to the Halloween. Under the conditions of the Energy Policy Act of 2005, daylight saving time starts on the second Sunday in March and ends on the first Sunday in November – a change put in place in part to allow children to trick-or-treat in more daylight.
Which states don't observe daylight saving time?
Nearly every U.S. state observes daylight saving time, with the exceptions of Arizona (although some Native American tribes do observe DST in their territories) and Hawaii. U.S. territories, including Puerto Rico, American Samoa, Guam and the U.S. Virgin Islands, do not observe daylight saving time.
How to prepare your body to 'spring forward'
The AASM encourages everyone to take the following steps to minimize the disruption:
- Get at least seven hours of sleep per night before and after the time change. Maintaining a consistent sleep routine is crucial.
- Gradually adjust your bedtime and rise time by shifting them 15-20 minutes earlier each night a few nights before the time change.
- Adjust the timing of daily routines that are “time cues” for your body, such as your mealtimes or exercise schedule.
- Set offline clocks ahead one hour on the evening of Saturday, March 8, and go to bed at your usual time. Online clocks will adjust automatically at 2 a.m. on Sunday, March 9.
- Head outdoors for early morning sunlight the week after the time change, as the bright light will help set your internal clock to the new time. This helps regulate sleep and alertness.
