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Daylight Savings Time Guide

Medically Reviewed by Dr. Sahil Chopra

In the United States, Daylight Savings Time occurs every year, from Mid-March to November. It’s a time of year many of us have strong feelings about, even though (or in part because) we don’t really understand the reasons why we practice it. In fact, most Americans don’t know the proper name is “Daylight Saving Time” without an “s.”

Did you also know Daylight Saving Time occurs in many countries around the globe? And that Benjamin Franklin may have had something to do with it?

There are a lot of interesting facts about Daylight Saving Time, and a growing body of research that suggests it may not be as good for us as we thought. In this guide, we dig into the details. Read on to learn all about Daylight Saving Time.

What is Daylight Saving Time?

Daylight Saving Time (DST) is the annual practice of setting our clocks forward by 1 hour ahead of standard time in the spring. DST occurs during the summer months, with the specific dates dictated by the government.


Daylight Saving Time (DST) is the annual practice of setting our clocks forward by 1 hour ahead of standard time in the spring.

DST is practiced differently across the globe, and countries and U.S. states have practiced it to varying extents over time, starting and ending it on different days or foregoing it altogether. In this section we’ll cover how DST works around the world.

How Daylight Saving Time Works

While the official date may change from year to year, Daylight Saving Time begins at 2am on the second Sunday in March in the United States. At that moment, all clocks move forward (or you change them manually when you wake up) to 3am, so we effectively “lose” one hour. Those who have a glass-half-full approach to life view it as jumping ahead one hour, earning DST its colloquial nickname of “Spring Forward.”

The switch takes place in the middle of the night so as to cause the least disruption to our lives. It’s late enough in the evening that people are home from their Saturday night, but it’s early enough to avoid interfering too much with people who work early shifts or attend church in the morning.

The whole point of Daylight Saving Time, and the reason it occurs during the summer, is to help us take advantage of more natural sunlight during the day—particularly in the early evenings. As the seasons change from winter to spring in the northern hemisphere, the Earth shifts on its axis closer toward the sun. This provides countries in the northern hemisphere with more sunlight day by day, eventually leading to the longest day of the year on June 21st, the summer solstice.

earth rotational axis during summer

By moving the clocks ahead 1 hour during the summer months, countries in the northern hemisphere—especially those furthest from the equator—enjoy more sunlight during the day. These countries conceivably get the most benefit from the time change, as they get significantly more sunlight.

" "Thanks to the earth’s rotational axis, countries in the northern hemisphere—especially those furthest from the equator—enjoy more sunlight during the day during DST." "

Who uses Daylight Saving Time?

Currently, less than 40% of countries participate in DST, a number which includes countries in both the Northern and Southern hemispheres. DST begins for Northern Hemisphere countries in the spring, between March and April, and ends in the fall, between September to November.

Did You Know?

Fewer than 40% of countries worldwide participate in DST.

Because summer occurs at the opposite time of year for Southern Hemisphere countries, they practice DST between September to November and March to April. Countries around the equator do not participate in DST, since their amount of sunlight stays relatively stable throughout the year.

The number of countries participating in DST continues to fluctuate. Some countries observe DST sporadically. One such example is Libya, who used it continuously from 1982 to 1989, then again in 1997 and 2013. Chile delayed the start date of DST twice, for a 1987 Pope visit and a 1990 presidential inauguration.

Some countries have given up DST completely. A few of the major countries who no longer participate in DST include Japan, India, and China.

In fact, not even all parts of a country may participate in DST. In the U.S., Hawaii and Arizona do not observe DST, and some Canadian provinces do not observe it. Today around 70 countries use DST in at least some part of their country.

In the map below, blue represents countries currently using DST, orange represents countries who formerly used DST, and red represents countries who never used DST.

which countries use daylight saving time

When does Daylight Saving Time begin and end?

The answer depends on the country. While DST usually takes place sometime between midnight and 3am, it begins and ends on different days around the world—sometimes months apart. Even within a country, the time may change on a different date every year, and not every region in the country may participate.  

To give you an idea of the variability around DST start and end times, below is an overview for just a handful of countries:

Continent Country Begin Date End Date
North America United States & Canada* Second Sunday in March First Sunday in November
Mexico First Sunday in April Last Sunday in October
Cuba Second Sunday in March First Sunday in November
South America Brazil* First Sunday in November Third Sunday in February
Paraguay First Sunday in October Last Sunday in March
Europe European Union Last Sunday in March Last Sunday in October
United Kingdom Last Sunday in March Last Sunday in October
Asia Jordan Last Friday in March Last Friday in October
Syria Last Friday in March Last Thursday in October
Oceania Australia* First Sunday in October First Sunday in April
New Zealand Last Sunday in September First Sunday in April

*Indicates a country where some states or provinces do not observe DST.

You may have noticed Africa missing from the above chart. Only a few places in Africa still use DST, including territories owned by Spain or Portugal like the Canary Islands and Madeira. Morocco was the last country to observe the time change, before switching to permanent DST in 2018. Other countries, including Egypt and Tunisia, formerly used DST but no longer observe it.

History of Daylight Saving Time

How did Daylight Saving Time begin in the first place? It all starts with Benjamin Franklin in 1784. During his time as the ambassador to France, Franklin wrote a lighthearted letter to The Journal of Paris, wherein he satirically complained of being woken up too early by the bright morning sun. In the essay he suggests Parisians change their sleep schedules to wake up at dawn, enabling them to save “by the economy of using sunshine instead of candles.” He even calculated the costs of candle wax for them:

benjamin franklin letter to paris about daylight saving time

However, Franklin’s was meant to be humorous, and merely suggested changing the Parisians’ sleep schedules—not switching clocks forward.

Over a century later, in 1907, an English builder and horseman William Willett published a pamphlet advocating moving the clocks forward 20 minutes a week for a period of 4 weeks in April. He wanted to grant people like himself more opportunities for daytime recreation and costs savings in electrical lighting. Even though he had champions like Winston Churchill by his side, Willett died in 1915 and never saw Parliament pass his idea.

It took the hardships of war for DST to finally pass. During World War I, countries needed coal to support the war efforts, but rations were running slim. In 1916, Germany became the first country to implement DST, with others like Britain following suit soon after.

" "Germany became the first country to implement DST in 1919." "

As you can see, despite the common myth, farmers had nothing to do with the founding of DST. In fact, they heavily opposed it, leading to its repeal in 1919 after the war was over. DST is actually very disruptive to farmers, since their schedules already follow the sun. With DST in place, their workday was delayed by an hour, as they had to wait longer for morning dew to evaporate from their hay. It was cut short on the other end, too, since employees continued to leave at the same time for dinner.

Since the 1919 repeal of national DST in the U.S., the time change has been regulated at a state and local level. Any changes to the practice are usually dictated by commercial interests (not farming ones).

Interesting Facts about Daylight Saving Time

Daylight Saving Time certainly has an interesting history, but the fun facts don’t stop there. Here are a few more trivia-worthy tidbits about this practice.

  1. It’s reversed the birth order of twins.
  2. Candy makers lobbied in the 1980s to push the end after Halloween.
  3. Bars stay open 1 hour later in the fall, and close 1 hour early in the spring.
  4. One Australian island only changes their clocks by 30 minutes.

It’s reversed the birth order of twins.

In November 2016, right after “Fall Back,” a pair of twin boys were born on either side of the time change. One boy was born at 1:39am and the other at 2:10am, or rather, 1:10 am. The second twin was younger by 31 minutes, but since his date of birth was recorded after the time change, his birth certificate says he’s 29 minutes older!

Halloween used to be much darker.

The end of Daylight Saving Time didn’t always take place in November in the U.S. It used to take place earlier, making Halloween a suddenly very dark night—which made parents nervous about their children’s safety, and candy makers very nervous about their sales.

In the 1980s, the National Confectors Association lobbied, along with golf and barbeque industries, to push the end of DST back a week into November. Their dreams weren’t answered until 2007, when President George W. Bush extended daylight saving time as part of the Energy Policy Act.

It makes bartending interesting.

In many large cities, it’s common for bars to stay open until 2am. In the fall, this coincides with Fall Back. While the bar can decide whether or not they want to close at the “normal” time or not, many decide to stay open, effectively giving partygoers an extra hour out on the town.

In the spring, partiers may be unhappy to hear, that means bars technically close one hour early, since the clock says 2am at 1am. Stay open later, and the bar could risk an after-hours service violation.

Not everyone uses the 1-hour standard.

The vast majority of countries participating in DST shift their time by 1 hour. But in one place in the world, time only shifts by 30 minutes. From April to October, residents of Lord Howe Island off the east coast of Australia are 30 minutes ahead of their time zone counterparts.

Benefits and drawbacks of Daylight Saving Time

Some countries continue to participate in DST because they believe the extra daylight is beneficial to society, perhaps resulting in fewer traffic accidents and more opportunity for outdoor exercise. Other countries don’t believe the tradeoff is worth it, considering the disruptions DST causes to a 24-hour, global economy, and growing research indicating an increase in workplace injuries and heart attacks in the first week following the spring time change.

To date the research suggests some clear benefits to DST, some clear disadvantages, as well as some inconclusive evidence as to whether DST has a positive, negative, or neutral effect on some things.

Benefits of DST Drawbacks of DST Benefit/drawback is unclear
More daylight
Reduced crime
Negative economic impact
Unpopular with the public
Disrupts sleep schedules
Energy conservation
Rate of traffic accidents

We discuss these benefits and drawbacks in detail below.

More daylight

One of the biggest arguments for DST is that we get more daylight in the evening. In theory, this gives us more time to spend outdoors with recreational activities like exercise, reduces the risk for car accidents since there are less people driving when it gets dark, and lessens our reliance on indoor lighting.

Energy conservation

This last point gets to the main reasons proponents give for sticking to DST: energy conservation. DST went into place during WWI, to reduce the burden on coal production. With more daylight, the theory goes, we need less energy resources. A U.S. Department of Transportation study from 2008 found that the total electricity savings are about 0.5% during each day of DST, which equates to a .03% reduction averaged over the course of the year.

Although, more recent studies suggest DST does the opposite; it may increase energy consumption. In 2008, Indiana researchers analyzed the effect on energy consumption during DST. In contrast to popular belief, they found that residential electricity demand actually increases during DST by 1%. While we might expect to save money on lighting since we have an extra hour of natural sunlight, in reality those costs seem to be offset by an increase in heating and air conditioning during the time people spend inside.

Add to all this the fact that today’s light bulbs are much more energy-efficient, so lighting is less of a drain on our total energy consumption than it was when DST first began.

Reduced crime

Putting the energy issue aside, there are other, unintended benefits to DST. Crime tends to occur more during the nighttime hours, and one 2015 study found that the daily robbery rate drops 7% following the beginning of DST in the spring, thanks to the sudden increase in daylight evening hours.

How were the study authors able to definitively attribute this to DST? The overall rate dropped overall by 7% but it dropped 27% during the hour that suddenly had sunlight.

Economic impact

One issue with DST is the lack of coordination among countries worldwide, despite their participation in a global economy. As we reviewed above, countries practice DST to varying extents (or not at all) at different times during the year. This makes it difficult to communicate globally, especially in the immediate days following a time change.

One 2011 study found a “surprisingly strong” negative relationship between DST and SAT scores. Using the estimate that a 1 point reduction in SAT scores is associated with a 1.5% difference in annual earnings, the researchers extrapolated the yearly economic impact could be as high as a $1.29 billion loss for a state like Indiana.

Lack of public enthusiasm

Only 55% of people don’t mind DST. The other 45% either find it somewhat or majorly disruptive to their lives. The arbitrary time change feels disruptive, and people get bummed about leaving for work in the darkness, or heading home in the darkness when it was previously light out.

Driving accidents

A few studies have been done regarding the relationship between DST and a rise or fall in traffic accidents. Thus far, the results are conflicting.

One 2001 study attributed a “small increase” in fatal accidents the Monday following DST to the resulting sleep deprivation from Spring Forward. Meanwhile, a 2010 study found that the increase in car crashes the day following DST was “not statistically significant,” and that overall DST led to fewer crashes due to improved visibility. Yet another study from 2010 found that DST had no impact on traffic accidents, positive or negative.

Finally, DST has a negative impact on your sleep, which trickles down to other health aspects of your life. We’ll review these in the following section.

Does Daylight Saving Time affect sleep?

Even in instances where we don’t realize it, the effect DST has on our sleep is significant and negative.

DST and sleep deprivation

A 2013 study published in Sleep Medicine found that while people generally believe they adjust to the new schedule quickly, it takes them at least a week to do so. During that time, they’ll experience fragmented sleep and an overall sleep loss that results in sleep deprivation during the spring change.

Perhaps more surprisingly, these negative effects to sleep persist during the fall time change, when people popularly believe they enjoy an extra hour of sleep. The same study found that people generally do not get extra sleep on that first night. Further, they continue to wake up earlier than their clocks would have them do so over the next five days, resulting in a net loss of sleep for the week.

The study authors found that the sleep deprivation in the week following both the beginning and end of DST indirectly led to higher rates of traffic accidents, and a disruption to bodily functions that shouldn’t be ignored.

What is Sleep Deprivation?

Many of us can acknowledge the effects of pulling an all-nighter, but not getting enough sleep for several days on end can be just as pernicious. All adults have a different sleep requirement that is just right for them, normal adult sleep duration ranges from 7 to 9 hours per night.


When we get less than that, we’re operating on a sleep-deprived mind and body. It’s harder for us to focus and process information, which affects our performance at work and school. It also slows down our reaction times, an important consideration for athletes and a potential factor in drowsy driving accidents related to DST. We also have a tougher time regulating our emotions and our mood, and our appetite goes haywire, craving junkier foods that don’t help our energy levels.


Sufficient quality sleep is critical to our overall health. Long-term sleep deprivation is linked to serious health conditions like diabetes and heart disease.

DST, heart health, and sleep

Speaking of heart health, several studies have documented a link between DST and an increase in acute myocardial infarction (heart attack), particularly in the first week after DST begins in the spring. There was also an increase after Fall Back, but it was smaller and more concentrated to the first weekday following the change.

heart attack increase after dst

The increase is not insignificant. A 2014 study found that acute myocardial infarctions increased by 24% on the Monday after Spring forward, with a reduction of 21% on the Tuesday after the fall change.

heart attacks after daylight saving time

Researchers attribute this increased heart attack risk to the sleep deprivation and circadian misalignment we suffer as a result of the time change.

Our circadian rhythms are popularly known as our sleep-wake cycle, but they dictate a variety of biological functions, including our appetite and energy levels. The word circadian comes from the Latin for “around day,” representing that these cycles roughly follow the patterns of the sun. When the time shifts as a result of DST, our daytime habits suddenly change and become misaligned with our natural circadian rhythms (which are still following the sun).

Sleep deprivation is associated with an increase in proinflammatory cytokine levels, cortisol levels (the stress hormone), and sympathetic activity. This can result in inflammation, a dangerous setup for a heart attack. For people with cardiovascular health conditions, this DST-related sleep deprivation increases their risk for experiencing a heart attack.

Researchers hypothesize this risk is aggravated in part because of the day of the week DST occurs. DST occurs on a Sunday, during the weekend. People already tend to stay up and wake up later on the weekends than they do during the week, so the shift to an earlier rising time feels more extreme, and may contribute to the higher incidence of acute myocardial infarction on the first weekday following the time change.

Even people without heart problems can be at risk of injury due to DST-related sleep deprivation. A 2009 study observed the sleep loss experienced among mine workers. They slept 40 minutes less on the Monday after Spring Forward—and witnessed a 5% increase in workplace injuries that day.

How to prepare for Daylight Saving Time

The best way to handle DST is to be prepared. Follow the tips below to make the transition a little bit easier.

Prepare for DST with these 7 steps

Follow these seven basic steps to prepare for DST.

1. Shift your sleep schedule by 15 minutes each day.

It’s hard to suddenly change your sleep schedule overnight. Instead, in the days leading up to Spring Forward, slowly start going to bed—and waking up—earlier by about 15 minutes each day.

2. Adjust your meal schedule, too.

Your body’s circadian rhythms don’t just dictate your sleep and energy levels; they also play a role in when you get hungry. Just like you adjust your sleep schedule, shift your meal and snack schedule by 15 minutes in the days prior.

3. Reset your clocks the night before.

The largest nuisance of DST is having to manually change your clocks. Since you might already be a bit grumpy on Sunday from not getting your usual hour of sleep, save yourself this annoyance by changing all your clocks ahead of time.

4. Avoid alcohol and caffeine too close to bedtime.

Alcohol and caffeine are both serious disruptors to sleep. Caffeine keeps you wired past bedtime, while alcohol makes you drowsy—only to wake you up too early. Be particularly careful with your consumption of these substances in the days preceding and following the time change.

5. Turn off the electronics.

Just like caffeine, electronics keep you wired. Your brain perceives the blue light in these devices as sunlight, which tricks it into staying up later than you should. Turn these off an hour before bed.

6. Ease the way with natural sleep aids.

Instead of watching TV, relax yourself to sleep with natural sleep aids. Melatonin is an extremely effective sleep aid that can help you fall asleep. It’s perfect for temporary situations when our sleep schedules shift, as during jet lag or DST. Another natural method is drinking a cup of tea before bed. Herbal bedtime teas contain sleep-promoting ingredients like chamomile or lavender to calm your mind and body for sleep.

7. Make your bedroom darker.

Another way to make yourself feel calmer so you can fall asleep faster is to make your bedroom a more restful environment. Cover your eyes with sleep masks. Wear earplugs to silence noise from roommates who aren’t preparing properly for DST. Block out ambient light with blackout curtains. You can get a dawn simulator alarm clock to help you rise naturally in the morning and give you an early AM energy boost.

Helping kids deal with the time change

For kids (as with pets), the time change can be confusing and unwelcome. Help your child adjust by following the tips above and the three below.

1. Explain the time change.

The time change will feel less sudden if you explain it to your child. Explain how the time changes every year. You may even find a way to make it sound exciting, like a special holiday, or make it a learning experience by using toy models of the earth and sun.

2. Shift their schedules, too, to the best extent possible.

While there are certain parts of your child’s schedule that are out of your control, such as school start times and extracurricular activities, you can shift their eating and sleep schedules by 15 minutes for 4 days leading up to the time change. If, once the time changes, they still feel out of sorts, be patient and recognize that it may take them a week or so to fully get used to it.

3. Get some exercise outdoors together in the sun.

The good thing about DST is it occurs on Sundays, which is hopefully a day both you and your kids have off. Take advantage of that free time to naturally synchronize your circadian rhythms using the sun. Spend time outdoors, getting exercise if possible, to wake yourselves up and help tire your bodies physically so you’re ready for bedtime when it comes.

What will happen with Daylight Saving Time in the future?

The number of countries practicing DST continues to change. Each year bills get proposed to adjust or change DST. Sometimes they get passed, and sometimes they don’t.

Here at Tuck, we don’t take sides in the ongoing debate for and against DST, but there are definitely some interesting things happening in the world revolving around this practice.

Here’s some of the latest news and legislation happening around DST.

In the United States:

In 2018, Florida passed the Sunshine Protection Act. This act would exempt Florida from the federal 1966 Uniform Time Act and transition Florida to adopt DST year-round—meaning that for half of the year, it would be 4 hours ahead of its counterpart on the West Coast.

The Uniform Time Act gives states the option to either adopt DST or to remain on standard time all year (as Arizona does). To switch to year-round DST, this Act needs to change. While the bill was approved in the Florida state Senate and House, it still needs to be approved by Congress. Until that happens, Florida will continue to practice DST like the rest of the states.

Similarly, in California, residents voted to approve Proposition 7 on the midterm ballot by nearly 60%. Because California had adopted DST through Proposition 12 in 1949, it needed to be repealed by voters before state legislature could take action toward changing DST in the state. Prop 7 repealed Prop 12, paving the way for California to move to year-round DST—once Congress modifies the Uniform Time Act.

Other states currently seeking exemptions from the federal Uniform Time act include Montana, Texas, and Nebraska.

In Europe:

When the European Union surveyed 4.6 million of its residents, they found 84% disliked seasonal time changes. Beginning at the end of October 2019 (or the end of DST in 2019), EU member countries could determine whether they want to move permanently to DST or stay on standard time.


The value of DST remains a heated debate. Clear benefits are the increase in evening daylight and resulting decrease in robbery crimes. However, DST does have negative impacts on our sleep and the economy. As for the effect of DST on energy consumption and traffic accidents, the evidence remains mixed.

Whichever side of the DST debate you’re on, it does appear that one side is winning out over the other, as more countries continue to drop DST in favor of a single time schedule year-round.

If you live somewhere that observes DST, the best thing you can do to minimize the impact to your sleep and your overall health is to prepare. Just like you might do to avoid jet lag, start gradually shifting your schedule to get used to the time change before it actually happens. Then, once it’s here, you’ll be a lot less tired and out of sorts than the rest of your friends.

If you’re interested in learning more about how environmental and time changes affect your sleep, read our guides to seasonal affective disorder, jet lag, and other sleep disorders.

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