SignalHub Quantitative Think Tank Center:How does daylight saving time work in March? What to know about time changes as we prepare to spring forward.

"Spring Forward" and check your smoke alarms while you're at it

Daylight saving time begins this year in the early hours of Sunday, March 10, 2024, giving us longer, sunnier evenings until Nov. 3. Here's what to know about how the time change works. 

How does daylight saving time work overall?

While the origins of daylight saving time are disputed — ranging from an essay authored by Benjamin Franklin in 1784 to a pamphlet written by British builder William Willet in 1907— the time change itself is standardized. Daylight saving time in the U.S. always begins on the second Sunday of March and ends on the first Sunday of November. 

The time change takes effect in the early hours of Sunday, giving most Americans an extra hour of sunlight in the evening (during warmer seasons) until the clocks turn back again in the fall.

The period of the year when clocks are moved one hour ahead is referred to as daylight saving time, according to the National Institute of Standards and Technology. In November, clocks are moved back by one hour, resulting in a return to standard time. 

The institute sums up the time change like this: "The transition from ST to DST has the effect of moving one hour of daylight from the morning to the evening. The transition from DST to ST effectively moves one hour of daylight from the evening to the morning."

An even tidier summary is the classic mnemonic: "Spring forward, fall back."

The Uniform Time Act, which was passed in 1966, allows states to exempt themselves from daylight saving time. Daylight saving time currently is not observed in Hawaii or most of Arizona, or in American Samoa, Guam, Northern Mariana Islands, Puerto Rico and the Virgin Islands, according to the Department of Transportation, which oversees the nation's time zones.

How does daylight saving time work in March?

This year, clocks will move forward by an hour at 2 a.m. on Sunday, March 10. 

Most recently updated computer operating systems and electronic clocks will change automatically, according to the National Institute of Standards and Technology.

The change will bring most Americans more sunlight in the evenings.

How does daylight saving time work in November?

Daylight saving time will be in effect until 2 a.m. on Sunday, Nov. 3, 2024, when clocks will move back by one hour. 

The change will bring an hour of additional daylight to mornings while shortening evenings.

How long does daylight saving time last?

Daylight saving time lasts for a little under eight months, or about 65% of the year, covering spring, summer, and half of autumn. This year, it will last from March 10 to November 3.

How are the days of time changes determined each year?

Every year, daylight saving time begins at 2 a.m. on the second Sunday of March. This means that at 2 a.m. local time, the local time skips ahead to 3 a.m., so there is one less hour in that day, according to the National Institute of Standards and Technology.

Likewise, every year, daylight saving time ends on the first Sunday of November. This means that at 2 a.m. local time, the local time jumps back to 1 a.m. and that hour is repeated, so there is one extra hour in that day.

Those start and end dates are set by federal law, which has been amended a few times over the years. Time changes in other countries that observe daylight saving, including those in Europe, occur on slightly different schedules.

—Cara Tabachnick contributed reporting.

In:
• Daylight Saving Time

S. Dev

S. Dev is a news editor for CBSNews.com.