Daylight Saving Time

Daylight saving time (DST) — called summer time in the UK and most of Europe — is the practice of setting clocks one hour forward in spring and one hour back in autumn. The key thing to understand: DST does not create extra daylight. The sun rises and sets at exactly the same astronomical moment regardless of what your clock says. What DST does is shift when that daylight falls relative to your daily schedule, moving an hour of morning light to the evening.

When do the clocks change?

The dates vary by region:

Australia and New Zealand observe DST too — but because they are in the Southern Hemisphere, their seasons are flipped, so their clocks spring forward in October (their spring) and fall back in April (their autumn).

Which countries don't observe DST?

The majority of the world's countries do not observe daylight saving time. Most of Africa, most of Asia (including China, Japan, India, and most of Southeast Asia), and most of the Middle East keep a fixed time year-round. In South America, most countries stay on standard time, though a few — notably parts of Brazil historically — have observed it. Even within countries that observe DST, there are exceptions: Arizona in the USA stays on standard time year-round (except for the Navajo Nation), as do Hawaii and several US territories.

How does DST affect sunrise and sunset?

When clocks spring forward in late March in London, sunrise suddenly shifts from around 06:00 to around 07:00 — a noticeably later start to the day. Sunset, however, moves from around 18:45 to 19:45, giving an extra hour of usable evening light. For many people this trade-off feels worthwhile in spring and summer. In autumn, when clocks fall back, the reverse happens: darker mornings become lighter, but evenings arrive an hour earlier.

The effect is most pronounced at high latitudes where the rate of daylight change is fastest. Near the equator, where daylight barely varies across the year, DST has almost no practical impact — which helps explain why tropical countries largely don't bother with it.

A brief history

The idea is often attributed to Benjamin Franklin, who in 1784 wrote a satirical essay suggesting Parisians could save candles by waking earlier — but he was joking. The first country to actually implement DST was Germany in 1916, during World War I, as a measure to save coal. The UK and other Allied nations quickly followed. The US adopted it during both World Wars and then made it permanent in 1966 with the Uniform Time Act.

The original justification — saving energy — has been questioned by modern research. Studies have generally found the energy savings to be modest at best, and in some climates non-existent, because heating and cooling demands often offset any lighting savings.

The debate about abolishing DST

The twice-yearly clock change is unpopular in many countries. Critics point to disrupted sleep, a documented spike in traffic accidents and heart attacks in the days following the spring change, and the general inconvenience of updating clocks and schedules. In 2019 the European Parliament voted to end the practice across the EU, leaving member states to choose permanently between summer time or standard time. As of 2026, however, no final date for abolition has been set, and the bloc remains divided on which permanent time to adopt. In the US, the Sunshine Protection Act — which would make DST permanent — has passed the Senate but has not become law.

Use the tool on the homepage to see exact sunrise and sunset times for your location, on any date — so you can always see how much daylight is actually available, regardless of what the clocks say.

What the clock change does not do

It is worth being blunt about this, because the misconception is widespread: moving the clock does not create, save or destroy a single minute of daylight. The sun rises and sets when the geometry says it will. All that changes is the number you have agreed to call that moment.

What the change actually does is reallocate daylight between the two ends of the waking day. Springing forward moves an hour of light from the early morning — when most people are asleep and cannot use it — to the evening, when they can. The total is untouched. On the day of the change itself, the amount of daylight differs from the day before by the usual couple of minutes and nothing more.

This is also why the effect is so uneven geographically. The further you are from the equator, the more daylight there is to reallocate in summer and the less the exercise matters in winter — and near the equator, where the day is twelve hours all year, there is nothing to gain at all. That is the main reason tropical countries almost universally do not bother.

Where you sit in your timezone matters more

For most people, the position of their town within its timezone has a larger effect on when the sun sets than daylight saving does — and it applies all year rather than half of it.

A timezone is nominally 15° of longitude wide but keeps a single clock, so solar noon at the western edge falls up to an hour later than at the eastern edge. Stack daylight saving on top and the divergence gets striking. Western Spain is the standard illustration: geographically it belongs under the same meridian as Britain, but it keeps central European time, so summer sunsets there fall close to 22:00 — with no more daylight than a comparable latitude elsewhere. The much-discussed Spanish habit of late meals is at least partly a rational response to a clock that runs ahead of the sun.

China takes the same idea to its limit: a single official time across a span that ought to hold five zones, so the sun can rise after 10:00 in the far west in winter. If you want to see where you personally stand, the solar noon figure on the front page is the honest answer — see also when it is lightest.

The evidence on whether it works

Daylight saving was introduced and repeatedly re-introduced on the argument that it saves energy. The modern evidence for that is weak. Lighting is a far smaller share of household electricity than it was in 1916, and the reduction in evening lighting is substantially offset by increased heating in darker mornings and, in warm climates, by additional air conditioning in longer, hotter evenings. Studies in the United States and Australia have found savings close to zero, and in some cases a small net increase.

The health picture is clearer and less encouraging. The spring transition is consistently associated with a short-term rise in heart attacks, strokes and road traffic accidents in the days immediately following, and with measurable sleep loss across the population. The autumn transition is largely benign and may be slightly protective. The mechanism is not mysterious: the body clock is set by light, and a one-hour jump desynchronises it from the clock on the wall for several days.

What is genuinely contested is the alternative. Permanent summer time gives brighter evenings year-round but pushes winter sunrise very late — after 09:00 across much of northern Europe, and past 10:00 in Scotland. Permanent standard time is what most sleep researchers advocate, because it keeps clock time closer to solar time and protects morning light, but it costs the long light evenings that make the current arrangement popular. Britain has tried permanent summer time once before, from 1968 to 1971, and abandoned it.

Where things stand

The European Parliament voted in 2019 to end mandatory seasonal clock changes, leaving each member state to choose a permanent time. Implementation has been stalled ever since, largely because a patchwork of neighbouring countries picking different permanent offsets would be worse than the status quo — and no coordinated decision has been reached. In the United States, similar federal proposals have repeatedly passed one chamber and stopped.

So for now the changes continue: the last Sunday in March and the last Sunday in October across the EU and UK, and the second Sunday in March and first Sunday in November in most of the US and Canada. Whatever happens next, the amount of daylight on any given date will be exactly what it was going to be — see what day length is for what actually sets it.

Frequently asked questions about daylight saving time

Does daylight saving time give us more daylight?

No. Moving the clock does not create or destroy any daylight — it only reallocates it, shifting an hour from the early morning to the evening. On the day of the change the total amount of daylight differs from the day before by the usual couple of minutes and nothing more.

When do the clocks change?

In the EU and UK, on the last Sunday in March and the last Sunday in October. In most of the United States and Canada, on the second Sunday in March and the first Sunday in November.

Is daylight saving time bad for you?

The spring transition is consistently associated with a short-term rise in heart attacks, strokes and road traffic accidents in the days that follow, and with measurable population-wide sleep loss. The autumn transition is largely benign and may be slightly protective.