Whether you savor the extra sunlight in the summer or dread the jarring time jump, daylight saving time is inevitable (at least in most parts of the United States). Here are 25 things you should know before making the semiannual change.
1. Benjamin Franklin was half-joking when he suggested daylight saving time.
“All the difficulty will be in the first two or three days; after which the reformation will be as natural and easy as the present irregularity [...] Oblige a man to rise at four in the morning, and it is more than probable he will go willingly to bed at eight in the evening; and, having had eight hours sleep, he will rise more willingly at four in the morning following.”
In one prophetic passage, he pitched the idea as a money-saver (though at the time people would have been conserving candle wax rather than electricity). To enforce the out-there plan, Franklin suggested taxing shutters, rationing candles, banning non-emergency coach travel after dark, and firing cannons at sunrise to rouse late-sleepers. While his essay clearly brought up some practical points, Franklin may have originally written it as an excuse to poke fun at the French for being lazy. He wrote that the amount of sunlight that goes wasted each morning would likely come as a shock to readers who “have never seen any signs of sunshine before noon.”
2. Official credit for the daylight saving time idea goes to an entomologist.
The first serious case for DST came from a peculiar place. While working at a post office by day, an entomologist who did most of his insect hunting at night soon became frustrated by how early the sun set during the summer months. He reasoned springing the clocks forward would allow more daylight for bug collecting—along with other evening activities. The clocks could be switched back in the winter when people (and bugs) were less likely to be found outdoors.
When the idea was proposed to a scientific society in New Zealand in 1895, it was panned for being pointless and overly complicated. Just two decades later, daylight saving time would begin its spread across the industrialized world.
3. Germany made daylight saving time the law.
In 1916, Germany became the first country to officially adopt daylight saving time. It was born out of an effort to conserve coal during World War I, and Britain, along with many other European nations, was quick to follow the Germans’ lead. It wasn’t until 1918 that the time change spread to the U.S. A year after entering the war, America began practicing DST as an electricity-saving measure. Most countries, including the U.S., ceased official observation of the switch following wartime.
4. Daylight saving time gained new popularity during the energy crisis.
The U.S. reconsidered DST in the 1970s, when, once again, the argument pivoted back to energy conservation. The oil embargo of 1973 had kicked off a nationwide energy crisis and the government was looking for ways to reduce public consumption. Daylight saving time was imposed in the beginning of 1974 to save energy in the winter months. Not everyone was enthusiastic about the change: Some of the harshest critics were parents suddenly forced to send their children to school before sunrise.
5. Daylight saving time may actually be an energy waster.
Despite daylight saving time’s origins as an energy-saving strategy, research suggests it might actually be hurting the cause. One 2008 study conducted in Indiana found the statewide implementation of DST two years earlier had boosted overall energy consumption by 1 percent. While it’s true that changing the clocks can save residents money on lighting, the cost of heating and air conditioning tend to go up. That extra hour of daylight is only beneficial when people are willing to go outside to enjoy it.
6. Daylight saving time might also be a health hazard.
Even if DST was good for your energy bill, that wouldn’t negate the adverse impact it can have on human health. Numerous studies show the extra hour of sleep we lose by springing ahead can affect us in dangerous ways: An increased risk of heart attack, stroke, susceptibility to illness, and seasonal depression have all been linked to the time change. Researchers have also reported increases in traffic crashes and workplace injuries associated with daylight saving time’s switch.
7. Daylight saving time can deter crime.
Though people love to complain about it, daylight saving time isn’t all bad news. One notable benefit of the change is a decrease in crime. One study published in 2015 found that the start of DST in the spring was associated with a drop in robberies.
8. Daylight saving time is not mandated by federal law.
DST has been widely accepted across the country, but it’s still not required by federal law. U.S. residents resistant to springing forward and falling back each year might consider moving to Arizona. The state isn’t exactly desperate for extra sunlight, so every spring they skip the time jump. This leaves the Navajo Nation, which does observe the change, in a peculiar situation. The reservation is fully located within Arizona, and the smaller Hopi reservation is fully located within the Navajo Nation. The Hopi ignore DST like the rest of Arizona, making the Navajo Nation a daylight-saving donut of sorts, suspended one hour in the future for half the year.
9. Daylight saving time starts at 2 a.m. for a reason.
Daylight saving time doesn’t begin at the stroke of midnight like you might expect it to. Rather, the time change is delayed until most people (hopefully) aren’t awake to notice it. By waiting until 2 a.m. to give or take an hour, the idea is that most workers with early shifts will still be in bed and most bars and restaurants will already be closed.
10. The candy industry lobbied for an extension of daylight saving time.
Until recently, losing an hour of daylight in the fall presented a problem for the candy industry. That’s because daylight saving time traditionally ended on the last Sunday in October, a.k.a. before Halloween night. Intense lobbying to push back the date went on for decades. According to one report, candy lobbyists even went so far as to place tiny candy pumpkins on the seats of everyone in the Senate in 1985.
In 2005, the National Association of Convenience Stores backed a move to extend DST to eight months. It argued that the extension would result in more daylight for trick-or-treaters and thus more candy sales. The law extending DST into November finally went into effect in 2007.
11. Different countries use different terms for daylight saving time.
When the clocks are moved an hour ahead in the UK, it’s called British Summer Time, or BST. When they go back, the UK is on Greenwich Mean Time. Europe uses Western European Summer Time (WEST), Central European Summer Time (CEST), and Eastern European Summer Time (EEST). In Ireland, there is Irish Standard Time, or IST.
12. Daylight saving time wouldn’t help countries near the equator.
The primary selling point of daylight saving time—that it conserves energy—appears to be an antiquated theory, namely because light bulbs and coal usage are not our main concerns anymore.
The California Energy Commission found the energy savings of extending DST by a month in 2007 to be 0.18 percent at best. In one example, while we may indeed keep our lights off longer, we counter that benefit by using air conditioners more during the hotter late-day hours. One analysis of 44 studies found a slight electricity savings, 0.34 percent, during the days when DST applies. The savings were highest in locations farther from the equator, while subtropical regions actually consumed more electricity because of DST.
13. The correct term is daylight saving (not savings) time.
For the sticklers out there, the correct phrase is daylight saving time, and it’s not capitalized. The U.S. Government Publishing Office Style Manual specifies no s in the name [PDF]. The online Thesaurus reminds us that the word saving is singular because it refers to saving time, as opposed to something like a savings account. However, it also says the term daylight savings time has become so popular that it’s generally accepted as a common variant in conversation.
14. For decades, states could implement their own daylight saving time.
The United States adopted daylight saving time in 1918, abolished it after World War I, then reinstated it in February 1942 during the World War II, when President Franklin Roosevelt established a year-round DST called “War Time.”
After World War II, states and towns could decide for themselves whether to use daylight saving time and when, which led to a free-for-all and lots of confusion about time zones from 1945 to 1966. The broadcasting industry, rail, airline, and bus companies in particular had a tough time publishing accurate schedules. Iowa had 23 start and end dates alone, and St. Paul, Minnesota, began daylight saving two weeks before nearby Minneapolis.
In 1966, Congress enacted the Uniform Time Act, which said that any state observing DST had to adhere to a uniform protocol that dictated when it began and when it ended. The Energy Policy Act of 2005 (which went into effect in 2007) extended daylight saving time by a month; it begins in March and ends the first Sunday in November.
15. Less than 40 percent of the world observes daylight saving time.
As of 2023, 71 countries use daylight saving time. Because countries close to the equator experience little fluctuation in the amount of daylight throughout the year, most of them don’t use DST; 38 countries in Africa have never used it.
Among the countries that do use DST, many have repealed it and reinstated it. Canada has used DST the longest, at 111 years; the U.S. has used DST for 106 years.
16. The push to observe daylight saving time year-round is growing.
The move to make daylight saving time permanent has gained traction the past few years. In 2018, Florida attempted to make daylight saving time permanent when its House and Senate passed legislation called the Sunshine Protection Act, and since then, more states have joined the fight.
States cannot implement DST year-round, however, because the federal Uniform Time Act mandates a synchronized schedule—basically, the same start and end date for any states that opt in. Therefore, state legislation only serves to ask the federal government for an exemption to the Uniform Time Act.
In March 2021, a bipartisan group of U.S. senators cosponsored the Sunshine Protection Act of 2021, which would make daylight saving time permanent (the current so-called “standard time” only lasts from November to March). The Senate passed the bill in 2022. As of 2023, the bill still needs to be approved by the House and the president.
17. Most farmers actually oppose daylight saving time.
A common myth states that daylight saving time was adopted to benefit farmers, but the opposite is true: farmers largely hate it. In fact, farmers opposed the move from the beginning because it wreaks havoc with their schedules; they had to rush crops to market—regardless of the time on the clock, they have to wait for the dew to evaporate off the hay in the morning. For dairy farmers, the time change throws the cows off, plus it could be difficult to manage the schedules of hired workers.
18. Department stores love daylight saving time.
While the farmers lobbied against daylight saving time, chambers of commerce and other business leaders have been all for it. Lincoln Filene, the department store owner who founded Filene’s Basement, lobbied hard for DST and even created promotional material that claimed the move was good for farmers.
In 1986, while campaigning to extend DST from six to seven months, grill and charcoal industries said they gained $200 million in sales with an extra month of DST.
19. The number of months of daylight saving time keeps growing.
Congress has extended the length of daylight saving time three times: once during a temporary extension during the energy crisis of the early 1970s, and then again in the 1980s and in 2007. Today, it runs for eight months, while standard time is just four.
20. Pets notice changes in humans’ behavior during daylight saving time.
Pets thrive on predictable schedules, and nothing is more important to them than mealtime and playtime. So when a pet with a set feeding schedule suddenly experiences a change—their owner gets up an hour later, delaying breakfast—they notice. Experts recommend a gradual shift to ease into the change, much like one that would benefit humans. This could include changing their mealtimes by 10 or 15 minutes leading up to the time change.
21. Daylight saving time is expensive for airlines and other modes of transportation.
When daylight saving time was lengthened by a month in 2007, the airline industry opposed it. The Air Transport Association estimated the cost to rearrange schedules to align U.S. flights with international travel would cost the industry $147 million. Trains also need to adjust, with Amtrak either making up for lost time in spring or stalling for an hour in fall.
22. The Network Time Protocol allows cell phones and other devices to update to daylight saving time automatically.
In the not-too-distant future, it might seem quaint to walk around the house turning clock hands forward or backward or resetting the digital clocks on our microwaves and ovens to adjust for the time change. Our cell phones, laptops, and other devices update automatically because of an internet protocol called Network Time Protocol, which synchronizes the clocks on computer networks.
Connected devices like cell phones and laptops request and receive time from a server that has gotten the information from an atomic clock or some other source for a precise time. These networks synchronize within a few milliseconds of universal coordinated time, or UTC. Because our devices are constantly communicating with cell towers and servers, they automatically adjust the time change when it occurs.
23. For decades, parts of Indiana observed daylight saving time, and other parts of the state opted out.
In April 2006, Indiana became the 48th state to observe daylight saving time statewide. The Hoosier state has had a somewhat convoluted experience with time zones; it fell within the Central Time Zone until 1961, when the Interstate Commerce Commission moved the demarcation line west and split the state into two time zones, Central and Eastern.
Five years later, the U.S. Department of Transportation assumed responsibility for time zones and again moved the lines. Most of Indiana fell within Eastern Standard Time while the Gary and Evansville areas remained on Central Time, also following daylight saving time in the summer. President Nixon signed the idea into law in 1972.
In 2004, Indiana governor Mitch Daniels pushed for statewide daylight saving time. After much back-and-forth and multiple votes, the state legislature finally passed the measure in 2005 by a 51-49 vote.
24. Some think that daylight saving time killed drive-in movie theaters.
More than 4000 drive-in movie theaters dotted the landscape in the mid-1960s. Theater owners banded together to oppose widespread adoption of daylight saving time in 1966, arguing that movies would start too late and hurt business. Today there are only about 330 drive-in theaters left in the U.S., and some enthusiasts blame the time difference.
25. A study found that most people lose 40 minutes of sleep when daylight saving time starts.
Christopher Barnes, an assistant professor of management and organization at the University of Washington, found that most people lose 40 minutes of sleep during the time change in spring, just enough to throw our body’s circadian rhythms off. Because it takes a few days to recover, the short-term effects of the change tend to fall on the Monday after the adjustment. Barnes also reported a marked increase in “cyberloafing,” or surfing the internet during work hours, on the Monday following the spring time change.
A version of this story originally ran in 2016; it has been updated for 2023.