Daylight saving time will begin on Sunday, Mar. 10, 2024 at 2 a.m. local time, when clocks will spring forward by one hour. This year's daylight saving time (sometimes erroneously called daylight SAVINGS time) ends on Nov. 3, 2024, when clocks fall back by an hour. In most of Europe, daylight saving time, or British Summer Time as the U.K. calls it, begins on the last Sunday in March, which is Mar. 31, 2024, and ends on the last Sunday in October (Oct. 27, 2024).

These spring and fall time changes continue a tradition started during World War I.

In 2022, the U.S. Senate overwhelmingly voted to make daylight saving time permanent, but the legislation stalled in the U.S. House. On March 2, 2023, U.S. Sen. Marco Rubio (R-FL) reintroduced the Sunshine Protection Act of 2023 to the 118th Congress, but it has idled since then.

Here's a look at when daylight saving time starts and ends during the year, so you know when to change your clock and not miss an important meeting. You'll also learn about the history of daylight saving time, why we have it now and some myths and interesting facts about the time change.

When does the time change?

Historically, daylight saving time (DST) has begun in the summer months and ended right before winter, though the dates have changed over time as the U.S. government has passed new statutes, according to the U.S. Naval Observatory (USNO).

So when does the time change? Starting in 2007, DST begins in the U.S. on the second Sunday in March, when people move their clocks forward an hour at 2 a.m. local standard time (so at 2 a.m. on that day, the clocks will then read 3 a.m. local daylight time). Daylight saving time then ends on the first Sunday in November, when clocks are moved back an hour at 2 a.m. local daylight time (so they will then read 1 a.m. local standard time).

(In most of Europe, daylight saving time begins on the final Sunday in March, and ends on the final Sunday in October.)

Why did daylight saving time start?

Benjamin Franklin takes the honor (or the blame, depending on your view of the time changes) for coming up with the idea to reset clocks in the summer months as a way to conserve energy, according to David Prerau, author of "Seize the Daylight: The Curious and Contentious Story of Daylight Saving Time" (Thunder's Mouth Press, 2005). By moving clocks forward, people could take advantage of the extra evening daylight rather than wasting energy on lighting. At the time, Franklin was ambassador to Paris, and he wrote a witty letter to the Journal of Paris in 1784, rejoicing over his "discovery" that the sun provides light as soon as it rises.

Even so, DST didn't officially begin until more than a century later. Germany established DST in May 1916, as a way to conserve fuel during World War I. The rest of Europe came onboard shortly thereafter. And in 1918, the United States adopted daylight saving time.

Though President Woodrow Wilson wanted to keep daylight saving time after WWI ended, the country was mostly rural at the time and farmers objected, partly because it would mean they lost an hour of morning light. (It's a myth that DST was instituted to help farmers.) And so daylight saving time was abolished until the next war brought it back into vogue. At the start of WWII, on Feb. 9, 1942, President Franklin Roosevelt re-established daylight saving time year-round, calling it "War Time."

After the war, a free-for-all system in which U.S. states and towns were given the choice of whether or not to observe DST led to chaos. And in 1966, to tame such "Wild West" mayhem, Congress enacted the Uniform Time Act. That federal law meant that any state observing DST — and they didn't have to jump on the DST bandwagon — had to follow a uniform protocol throughout the state in which daylight saving time would begin on the first Sunday of April and end on the last Sunday of October.

Then, in 2007, the Energy Policy Act of 2005 went into effect, expanding the length of daylight saving time to the present timing.

Why do we have daylight saving time?

Fewer than 40% of the world's countries observe daylight saving time, according to timeanddate.com. However, those who do observe DST take advantage of the natural daylight in the summer evenings. That's because the days start to get longer as Earth moves from the winter season to spring and summer, with the longest day of the year on the summer solstice. During the summer season in each hemisphere, Earth, which revolves around its axis at an angle, is tilted directly toward the sun.

Related: Read more about the science of summer.

As Earth orbits the sun, it also spins around its own imaginary axis. Because it revolves around this axis at an angle, different parts of our planet experience the sun's direct rays at different times of the year, leading to the seasons. (Image credit: BlueRingMedia / Shutterstock.com)Regions farthest away from the equator and closer to the poles get the most benefit from the DST clock change, because there is a more dramatic change in sunlight throughout the seasons.

Research has also suggested that with more daylight in the evenings, there are fewer traffic accidents, as there are fewer cars on the road when it's dark outside. More daylight also could mean more outdoor exercise (or exercise at all) for full-time workers.

The nominal reason for daylight saving time has long been to save energy. The time change was first instituted in the U.S. during World War I, and then reinstituted again during WW II, as a part of the war effort. During the Arab oil embargo, when Arab members of the Organization of Petroleum Exporting Countries (OPEC) stopped selling petroleum to the United States, Congress even enacted a trial period of year-round daylight saving time in an attempt to save energy.

But the evidence for any significant energy savings is slim. Brighter evenings may save on electric lighting, said Stanton Hadley, a now-retired senior researcher at Oak Ridge National Laboratory who helped prepare a report to Congress on extended daylight saving time. But lights have become increasingly efficient, Hadley said, so lighting is responsible for a smaller chunk of total energy consumption than it was a few decades ago. Heating and cooling probably matter more, and some places may need air-conditioning for the longer, hotter evenings of summer daylight saving time.

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Hadley and his colleagues found that the four weeks of extra daylight saving time that went into effect in the United States in 2007 did save some energy, about half of a percent of what would have otherwise been used on each of those days, they said in a report to Congress published on Sept. 30, 2020. However, Hadley said, the effect of the entire months-long stretch of daylight saving could very well have the opposite effect.

A 1998 study in Indiana before and after implementation of daylight saving time in some counties found a small increase in residential energy usage. Temporary changes in Australia's daylight saving timing for the summer Olympics of 2000 also failed to save any energy, a 2007 study found.

Part of the trouble with estimating the effect of daylight saving time on energy consumption is that there are so few changes to the policy, making before-and-after comparisons tricky, Hadley told Live Science. The 2007 extension of daylight saving time allowed for a before-and-after comparison of only a few weeks' time. The changes in Indiana and Australia were geographically limited.

Ultimately, Hadley said, the energy question probably isn't the real reason the United States sticks with daylight saving time, anyway.

"In the vast scheme of things, the energy saving is not the big driver," he said. "It's people wanting to take advantage of that light time in the evening."

What places observe daylight saving time?

U.S. daylight saving time

Most of the United States and Canada observe DST on the same dates with a few exceptions. Hawaii and Arizona are the two U.S. states that don't observe daylight saving time, though Navajo Nation, in northeastern Arizona, does follow DST, according to NASA. The U.K. also observes daylight saving time.

Over the years, state legislatures have considered at least 450 bills to establish year-round daylight saving time, according to the National Conference of State Legislatures. And as of 2022, at least 19 states had introduced legislation to make standard time permanent, doing away with DST all together. However, the U.S. Congress would have to amend the Uniform Time Act (15 U.S.C. s. 260a) to authorize states this allowance, according to The New York Times.

Canada daylight saving time

Nine of Canada's 10 provinces observe daylight saving time. The provinces and territories in Canada that stay on standard time all year include: Some regions of the province of British Columbia, parts of Saskatchewan, northwest Ontario and east Quebec, according to timeanddate.com. Meanwhile, Yukon made DST permanent in 2020. The locations in British Columbia that don't use DST include: Chetwynd, Creston, Dawson Creek, Fort Nelson and Fort St. John; in Saskatchewan, only Creighton and Denare Beach observe DST, according to timeanddate.com.

Europe daylight saving time

Most of Europe currently observes daylight saving time, which began at 1 a.m. GMT on the last Sunday in March. Daylight saving time ends (winter time) at 1 a.m. GMT on the last Sunday in October, or Oct. 29, 2023, when clocks were moved back an hour. DST will begin again on Sunday, March 31, 2024, according to timeanddate.com.

Most European countries observe DST, with the exception of Russia, Iceland and Belarus, according to timeanddate.com. In the United Kingdom, DST is called British Summer Time (BST).

DST is called Central European Summer Time (CEST) in: Austria, France, Germany, Italy, Hungary, Norway, Poland, Spain and Switzerland. Daylight saving starts at 2 a.m. local time for these countries, when clocks are moved ahead an hour to 3 a.m. The same 2 a.m. clock change is followed for Bulgaria, Estonia, Finland, Greece, Latvia, Lithuania and Romania, which call DST Eastern European Summer Time (EEST).

During summers in Ireland, DST is called Irish Standard Time (IST) and it begins at 1 a.m. local time, when clocks are moved ahead an hour to 2 a.m. The same clock change occurs in the Canary Islands, the Faroe Islands and Portugal, which call DST Western European Summer Time (WEST). However, even the European Union may propose an end to clock changes, as a recent poll found that 84% of 4.6 million people surveyed said they wanted to nix them, the Wall Street Journal reported. If the lawmakers and member states agree, the EU members could decide to keep the EU in summer time or winter time, according to the WSJ.

Southern Hemisphere DST

The DST-observing countries in the Southern Hemisphere — in Australia, New Zealand, South America and southern Africa — set their clocks forward an hour sometime during September through November and move them back to standard time during the March-April timeframe.

Australia, being such a big country (the sixth-largest in the world), doesn't follow DST uniformly: New South Wales, Victoria, South Australia, Tasmania and the Australian Capital Territory follow daylight saving, while Queensland, the Northern Territory (Western Australia) do not, according to the Australian government. In the observing areas, DST begins on the first Sunday in October — Oct. 6, 2024 — and it ends on the first Sunday in April — or April 7, 2024.

Daylight saving time myths

Turns out, people tend to have more heart attacks on the Monday following the "spring forward" switch to daylight saving time. Researchers reporting in 2014 in the journal Open Heart, found that heart attacks increased 24% on that Monday, compared with the daily average number for the weeks surrounding the start of DST.Before the Uniform Time Act was passed in the United States, there was a period in which any place could or could not observe DST, leading to chaos. For instance, if one took a 35-mile bus ride from Moundsville, West Virginia, to Steubenville, Ohio, he or she would pass through no fewer than seven time changes, according to Prerau. At some point, Minneapolis and St. Paul were on different clocks.A study published in 2009 in the Journal of Applied Psychology showed that during the week following the "spring forward" into DST, mine workers got 40 minutes less sleep and had 5.7% more workplace injuries than they did during any other days of the year.Pets may notice the time change, as well. Since humans set the routines for their fluffy loved ones, dogs and cats living indoors and even cows are disrupted when, say, you bring their food an hour late or come to milk them later than usual, according to Alison Holdhus-Small, a research assistant at CSIRO Livestock Industries, an Australia-based research and development organization.The fact that the time changes at 2 a.m. at least in the U.S., may have to do with practicality. For instance, it's late enough that most people are home from outings and setting the clock back an hour won't switch the date to "yesterday." In addition, it's early enough not to affect early shift workers and early churchgoers, according to the WebExhibits, an online museum.

Additional resources

Teacher Planet has lots of worksheets and lesson ideas to help kids learn about daylight saving time. The History Channel has a 1-hour video on the history of daylight saving time. In this Smithsonian Magazine feature, you'll learn about a time when the U.S. had year-round DST.

Editor's note: This article was updated on Feb. 15, 2024, to include accurate information about daylight saving time changes during 2024.