The idea in one sentence
Daylight saving time moves the clock forward in spring so an hour of daylight shifts from early morning, when most people are asleep, to the evening, when they can use it. In autumn the clock goes back to standard time. Spring forward, fall back. That's the whole trick.
Where it came from
Benjamin Franklin joked in 1784 that Parisians could save candles by getting up earlier. The serious proposals came later, from George Hudson, a New Zealand entomologist who wanted more daylight after work to collect insects, and William Willett, a British builder who was annoyed that London slept through summer sunrises. Neither lived to see it adopted. What actually got it done was war. Germany brought in DST in 1916 to save coal, and most of the world followed within two years. Since then it has been adopted, dropped and adopted again many times. The United States tried year-round DST in 1974 and gave up after one winter of pitch-dark school mornings.
Who uses it, and who quit
About a third of the world's countries observe DST, mostly in North America and Europe. Most of Africa and Asia never took it up or dropped it. Near the equator, day length barely changes across the year, so there's nothing to save. Japan, India, China and the northern half of Australia don't use it. In the US, Hawaii and most of Arizona stay on standard time all year. The European Union voted in 2019 to end the clock changes and still hasn't done it, which tells you the hard part of abolishing DST isn't the vote. It's choosing which time to keep.
What the clock change does to people
The spring change is a one-hour dose of jet lag given to a whole country at once. Studies have found short-term rises in heart attacks, workplace accidents and car crashes in the days after it, along with worse sleep. Sleep scientists, including the American Academy of Sleep Medicine, mostly favor permanent standard time, because morning light does more for the body clock than evening light. The autumn change is gentler. An extra hour of sleep bothers almost nobody.
Getting through the switch
- Move bedtime 15 or 20 minutes earlier for a few nights before the spring change instead of taking the whole hour at once.
- Get outside in the morning light on the days after the switch. Nothing resets the body clock faster.
- Watch your meetings. DST dates differ between countries, so for a few weeks each spring and autumn the gap between New York and London changes, and that quietly breaks recurring international calls. The converter and meeting planner both apply each region's real rules.
- Fire services suggest testing your smoke alarms every time you change the clocks. Worth keeping as a habit whatever your country decides.
Want to know what time it is anywhere right now, DST included? The world clock always uses the current rules.