Twice a year, much of the world moves its clocks by an hour. The idea is older than most people think, and its history includes a satirical letter, an insect collector, two world wars and a continuing political debate.
An early joke about candles
In 1784 Benjamin Franklin, then in Paris, wrote a humorous letter to a newspaper suggesting that Parisians could save money on candles if they got up earlier in the summer and used the morning daylight. He did not propose changing the clocks, and the letter was meant as a joke, but it is often cited as the first discussion of the idea.
The first serious proposal came a century later. In 1895 George Hudson, an entomologist in New Zealand, suggested moving the clocks forward by two hours in summer so he could have more daylight to look for insects after work.
William Willett and the waste of daylight
In 1907 the British builder William Willett published a pamphlet called The Waste of Daylight. He argued that millions of people slept through the best hours of summer mornings, and he proposed moving the clocks forward in small steps of twenty minutes during April. Parliament debated the plan but did not adopt it, and Willett died in 1915.
The First World War
Germany and Austria-Hungary were the first to introduce daylight saving time nationally, on April 30, 1916, in order to save coal during the war. Britain followed in May 1916, and many other countries introduced it within months, including Norway. The United States adopted it with the Standard Time Act of 1918, but repealed it a year later after farmers objected.
After the war many countries dropped it again, and the clocks were used in some cities and not in others, which gave the United States a patchwork of local rules for decades.
The Second World War and the energy crisis
During the Second World War daylight saving time came back. The United States ran year-round War Time from February 1942 until September 1945, and Britain used double summer time, two hours ahead of Greenwich, in the summers.
In the 1970s the oil crisis made energy saving relevant again, and several European countries introduced summer time for good. The United States tried year-round daylight saving time in 1974, but it was dropped after the first winter because children were going to school in the dark. Norway has had summer time every year since 1980.
Harmonizing the dates
For a long time, countries in Europe changed their clocks on different days, which caused trouble for train timetables and flights. The European Community fixed the dates in the 1980s, and from 1996 summer time in the whole union ends on the last Sunday in October. It begins on the last Sunday in March.
In the United States the Uniform Time Act of 1966 set common rules, and in 2007 the period was extended so that it now runs from the second Sunday in March to the first Sunday in November.
Arguments for and against
Supporters say that daylight saving time gives more light in the evening, which people use for outdoor activity, shopping and lower electricity use for lighting. Critics point out that the energy savings are small and in some studies not there at all, because people use more heating in dark mornings and more air conditioning in light evenings.
Some studies link the spring change to a short rise in sleep problems and accidents on the following days, although the evidence is mixed. Others point out that the change itself is a nuisance for everyone who works with schedules.
Countries that stopped
Russia introduced permanent summer time in 2011 and then permanent winter time in 2014, after dark winter mornings proved unpopular. Turkey stopped changing in 2016 and now stays on summer time all year. Mexico abolished daylight saving time for most of the country in 2022, and Brazil in 2019.
Countries close to the equator never use it, because day length hardly changes.
The debate today
In 2018 the European Commission proposed ending the clock changes after a public survey in which millions of Europeans voted for abolishing them. The European Parliament agreed in 2019, but member states have not agreed on whether to stay on summer or winter time, so for now the clocks still change twice a year.
You can see when the next change happens in your city with the clock and time zone tools on this site.