Twice a year, hundreds of millions of people change their clocks. Most of them could not say who started the practice or why. The story is less tidy than the usual explanations suggest, and it is still being argued about in the US Senate and in Brussels.
Benjamin Franklin did not invent daylight saving time. In 1784 he wrote a humorous letter to a Paris newspaper, suggesting that Parisians could save candles by getting out of bed earlier. It was a joke about lazy city dwellers, not a proposal to change clocks.
Daylight saving was also not created for farmers. Cows and crops follow the sun, not the clock, and farm groups were among the strongest opponents of the idea when it was first introduced in the United States.
The serious case began with a New Zealand entomologist, George Hudson, who proposed a two-hour shift in 1895 so he could collect insects after work. In 1907 a British builder, William Willett, published a pamphlet called "The Waste of Daylight". He argued that people slept through bright summer mornings and wanted clocks advanced in small steps through spring. Parliament debated the idea but did not adopt it.
A Canadian town got there first. In 1908 Port Arthur, in Ontario, became the first place in the world known to move its clocks forward for the summer. It was a local experiment, though, and it was dropped.
Daylight saving became real in the First World War. On 30 April 1916 Germany moved its clocks forward to save coal, and Britain followed on 21 May. Other European countries did the same within months. The United States adopted it in 1918 as part of the Standard Time Act. Farmers and others objected, and Congress repealed it in 1919 over President Wilson's veto.
In the Second World War the United States ran on year-round "war time" from 1942 to 1945. After that the picture became messy. Cities and states picked their own dates, which made broadcasting and transport schedules a nightmare. The US finally standardised the rules in the Uniform Time Act of 1966.
The 1973 oil crisis made energy saving urgent again. The US tried year-round daylight saving time in the winter of 1974, but the experiment was cut short after complaints about dark winter mornings, especially for children walking to school. Britain tried something similar from 1968 to 1971, staying on summer time all year, and dropped it after objections from Scotland. Both cases show a pattern: permanent summer time is popular in autumn, and unpopular by January.
The original argument was that more evening daylight means less electric lighting. The evidence today is mixed. Some studies find a small saving, some find none, and a well-known study of Indiana found that household electricity use rose slightly rather than fell, because extra air conditioning and heating on dark mornings cancelled out the lighting saving. Modern homes use energy for many things besides lights, so the effect is small whichever way it goes.
Sleep researchers are more concerned about the clock change than economists are. The abrupt shift disrupts sleep for a few days, and the spring change is linked in several studies to a short-term rise in some health problems. The American Academy of Sleep Medicine argues that if clocks stop changing, the better choice is permanent standard time, because it keeps the sun's timing closer to the body clock. Supporters of permanent daylight time respond that later sunsets help people be active and shop after work.
Only about a third of countries still use daylight saving time, and most of them are in Europe and North America. Many others have recently stopped. Turkey, Russia, Brazil, Mexico and Iran have all abolished it in the past fifteen years or so, which our guide to clock changes in 2026 and 2027 covers in more detail. Most of Africa and Asia never adopted it, and cities such as Tokyo, Singapore and Dubai keep one time all year.
In the United States, the House passed the Sunshine Protection Act in July 2026, which would make daylight time permanent, but the Senate has not voted, so the clocks still go back on 1 November. Around 19 states have passed laws ready to adopt permanent daylight time if Congress allows it. Federal law lets a state opt out of daylight saving time, as Hawaii and most of Arizona have done, but it does not let a state adopt permanent daylight time.
In the European Union, Parliament voted in 2019 to end seasonal changes, but member states disagree on which time to keep, and the plan has stalled. A split is the real fear: if neighbouring countries picked different permanent times, borders would have hour-long gaps year-round.
The reason both sides have not simply won is that "stop changing" is only half a decision. The other half is which time to keep. Permanent summer time means very dark winter mornings in the north. Permanent winter time means sunsets as early as 16:00 in some places in December. Whatever is chosen, someone loses, which is why a practice invented in wartime still survives more than a century later.
To see how time zones themselves developed, read our history of how the world agreed on the time.