Daylight saving time explained: when the clocks change and why

Twice a year, clocks in much of North America and Europe jump by an hour. Daylight saving time (DST) shifts an hour of daylight from the early morning to the evening during the longer days of spring and summer. Here is how it works and when it happens.

Spring forward, fall back

• When DST starts, clocks move forward one hour. At 2:00 a.m. local time the clock jumps to 3:00 a.m., so that night is one hour shorter and evenings become lighter.
• When DST ends, clocks move back one hour. At 2:00 a.m. the clock returns to 1:00 a.m., so 1:00–2:00 a.m. happens twice and you get an extra hour of sleep.

Phones and computers change automatically. Ovens, car clocks and wall clocks usually need to be changed by hand.

United States and Canada

Since 2007, most of the US has observed DST from the second Sunday in March to the first Sunday in November, a schedule set by the Energy Policy Act of 2005. Canada follows the same dates in the provinces that observe DST.

Exceptions: Hawaii and most of Arizona stay on standard time all year (the Navajo Nation in Arizona does observe DST), as do the US territories of Puerto Rico, Guam, American Samoa, the US Virgin Islands and the Northern Mariana Islands. Most of Saskatchewan in Canada also stays on standard time.

Europe

The European Union and the United Kingdom change clocks on the last Sunday in March and the last Sunday in October, at 01:00 UTC everywhere at once. That means that for a few weeks each spring and autumn, the time difference between Europe and North America is one hour different from usual. New York is normally five hours behind London, but for those few weeks it is only four.

Places that don't use DST

Most countries near the equator see little change in day length and don't use DST. Most of Asia and Africa do not change their clocks, including China, India, Japan and Pakistan. Pakistan tried daylight saving time in 2002 and again in 2008–2009 but no longer uses it. In the Southern Hemisphere, countries that do observe DST, such as Australia's southern states, New Zealand and Chile, change their clocks in the opposite months, because their summer falls from December to February.

Where did it come from?

Benjamin Franklin is often credited with the idea after a 1784 essay, but it was satire: he joked that Parisians could save candles by getting up earlier. Modern DST was first adopted nationwide by Germany and Austria-Hungary in 1916, during the First World War, to save fuel, and the United Kingdom, the United States and other countries soon followed. The US made it standard, with nationwide rules, under the Uniform Time Act of 1966, and states may opt out.

The debate

Supporters say lighter evenings encourage outdoor activity and shopping and may reduce some traffic accidents. Critics point to studies linking the spring change to disrupted sleep and a short-term rise in heart problems and accidents, and question whether it saves energy at all. Several US states have passed laws to adopt permanent DST if Congress allows it, and the European Parliament voted in 2019 to end seasonal clock changes, although that plan has not been implemented. For now, the twice-yearly change continues.

Tips for the change

• Shift bedtime by 15 minutes a day for a few days before the spring change.
• Get morning daylight after the change to reset your body clock.
• Double-check meeting times with people in other countries during the weeks when US and European schedules don't match. Our time zone converter accounts for DST automatically.