What Is Daylight Saving Time (DST)? A Plain-English Guide

Daylight saving time means that for roughly seven months a year the clocks run one hour ahead of the time that would otherwise apply. Nothing about the sun changes. What changes is the label on the clock: a sunrise that would have been at 04:45 is now recorded as 05:45, and a sunset at 20:45 becomes 21:45.

The name is slightly misleading. No daylight is saved, because the number of hours of daylight is set by the Earth's tilt. DST only moves daylight from the early morning, when most people are asleep, to the evening, when most are awake. The correct term is daylight saving time, singular, not daylight savings time.

In the UK the standard time is Greenwich Mean Time (GMT, which is the same as UTC+0). The summer time is British Summer Time (BST, UTC+1). The clocks go forward at 01:00 GMT on the last Sunday of March, which becomes 02:00 BST, and go back at 02:00 BST on the last Sunday of October, which becomes 01:00 GMT.

In 2026 the clocks go forward on Sunday, 29 March 2026 and back on Sunday, 25 October 2026. In 2027 they go forward on Sunday, 28 March 2027 and back on Sunday, 31 October 2027. Because the rule is fixed, these dates can be worked out many years ahead, and our clock-change page lists them for the next ten years.

BST lasts about 210 days a year and GMT about 154 days, so the UK spends a little more than half the year on summer time.

The European Union moves its clocks at the same instant everywhere: 01:00 UTC on the last Sunday of March and the last Sunday of October. That is 02:00 GMT in London, 03:00 CET in Paris and Berlin and 04:00 EET in Athens. Because the UK uses the same rule, the gap between London and most of Europe never changes during the year.

The United States and Canada use a different rule. Clocks go forward at 02:00 local time on the second Sunday of March and back on the first Sunday of November. In 2026 that is Sunday, 8 March 2026 and Sunday, 1 November 2026. For a few weeks each spring and autumn the UK and the US are on different settings, and the time difference with New York drops from five hours to four.

Australia and New Zealand are in the southern hemisphere, so their summer is our winter. They put the clocks forward in October (spring) and back in April (autumn), which makes the gap with the UK move twice a year in a different pattern again.

Most of the world does not change its clocks. Countries close to the equator have almost constant day length all year, so shifting the clocks has little to offer. Russia, Turkey, Belarus and Iceland in Europe, and most of Asia and Africa, stay on one time all year. India, China and Japan do not use DST. Within the US, Arizona (apart from the Navajo Nation) and Hawaii do not change.

Some places have changed their minds. Russia moved to permanent summer time in 2011, then to permanent standard time in 2014. Turkey moved to permanent UTC+3 in 2016. Mexico abolished DST in most of the country in 2022.

The idea is usually credited to the British builder William Willett, who in 1907 published a pamphlet called The Waste of Daylight and campaigned for the clocks to be moved forward in summer. Germany was the first major country to adopt the practice, on 30 April 1916, to save fuel during the First World War. Britain followed with the Summer Time Act, and the first British Summer Time began on 21 May 1916.

The practice was dropped and revived in many countries over the following decades. The UK used double summer time during the Second World War, and from 1968 to 1971 ran an experiment of staying on BST all year. Within the EU the dates were standardised so that all members change on the last Sunday of March and October, and an EU directive in 2000 made that rule permanent.

The original argument was that lighter evenings reduce the need for lighting. Modern evidence is mixed. Lighting is a small share of household energy, and heating and air-conditioning patterns shift when the clock does. Studies in different countries have found savings of a fraction of one percent, no effect, or small increases, so energy is no longer the main argument for either side.

Losing an hour of sleep in spring is harder than gaining one in autumn. Several studies have found short-term rises in sleep disruption, workplace injuries and, in some analyses, heart attacks in the days after the spring change. Sleep-medicine organisations in the US have argued for permanent standard time rather than permanent summer time because morning light is better aligned with the body clock.

The effects are small for most healthy adults and fade within a week, but they are why shift workers, parents of young children and people who rely on a strict medication schedule often plan ahead for the change.

The mnemonic is simple: in spring, clocks spring forward one hour; in autumn (fall), they fall back one hour. Forward means you lose an hour of sleep and gain evening light. Back means you gain an hour in bed, and the evenings get dark early.