When do the clocks go back in 2021?

Marking the end of British Summer Time, the clocks go back in October, giving us an extra hour in bed. But why do the clocks change?

In autumn 2021 the clocks will go back on 31 October at 2am.

Find out more about British Summer Time

On the last Sunday of October the clocks 'fall back': they go back by one hour.

It may feel like a long time since the blue skies of summer, but this marks the end of British Summer Time (BST). It also means an extra hour in bed.

Clocks on smart phones should update automatically, but older analogue clocks need changing manually. At the Royal Observatory in Greenwich, we even have sundials which need changing...

An easy way to remember which way the clocks change is to think of the seasons: in spring the clocks ‘spring forward', and in autumn they 'fall back'.

Do other countries change the clocks?

About 70 countries have some form of daylight saving time, but it varies from region to region.

Much of Europe and North America, as well as parts of South America and Australasia, change their clocks. However, many countries in Africa and Asia situated around the equator do not change the time.

The USA has daylight saving time, but not all states change their clocks. Arizona does not use DST (apart from the semi-autonomous Navajo Nation), and neither does Hawaii. Indiana introduced daylight saving time in 2006.

In the United States, the clocks go back on 7 November 2021

In March 2019, the European Parliament backed a proposal to end the practice of changing the clocks in European Union states. If the proposal is adopted, EU nations could change the clocks for the last time in 2021.

Why do the clocks change?

The clocks go back to revert to Greenwich Mean Time (GMT) which was in place before British Summer Time started in March.

The reason the clocks go forward and back is because of a campaign at the beginning of the 20th century, which successfully argued in favour of changing the clocks during the summer months to avoid wasting time in the morning.

Today people argue that changing the clocks will be good for:

  • reducing energy consumption for environmental reasons
  • having longer evenings to support leisure and tourism
  • encouraging people to exercise more outdoors
  • reducing road accidents.

Aside from the obvious inconvenience of changing the clocks twice a year, opponents have presented different arguments against daylight saving time, from safety concerns about darker mornings to farmers expressing concern about the effect of changing routines for livestock.

Others argue that changing the clocks is now redundant given that many of us spend most of our time in well-lit homes, shops and offices, where the amount of daylight makes little difference to our lives.

Similarly, the economic and environmental advantages can vary: for some warmer regions, it’s thought that longer evenings may actually increase energy consumption as people use air-conditioning units for more hours.

It’s an ongoing debate that strongly depends on people’s geographical location, occupation and lifestyle.

Greenwich Park and view over London in snow, with Queen's House and National Maritime Museum

Why do the clocks go back at the weekend?

This pattern of change was chosen because it occurs on a Saturday night/Sunday morning and would therefore be the least disruptive option for schools and businesses. 

What happens if I'm working when the clocks go back?

Of course, not everyone is tucked up in bed at 2am; employees who are scheduled to work a night shift at this time may find themselves working an extra hour when the clocks go back to 1am.

Night workers are often advised to check their contracts and discuss the situation with their employer. By law however, night workers must not work more than an average of 8 hours in a 24-hour period.

Will my phone automatically update the time?

Most devices with internet connection, such as smartphones, should automatically update. However, watches and clocks in cars and kitchens for example may not change automatically, so make sure you are ready to wind back.

Curator of the Royal Observatory, Louise Devoy, explains what happens in Greenwich when the clocks change:

Actually, I have very little work to do when the clocks change! We deliberately keep most of our historic clocks on GMT all year round as they were mainly used before the first daylight saving came into effect in 1916. Visitors arriving at the Observatory in the summer are often confused by the apparent delay shown on the Shepherd Gate Clock but as Britain’s first public clock to show GMT, we’re proud to continue this tradition.

The most significant change is our Dolphin sundial which needs to be adjusted four times a year: at the solstices (June and December) and when the clocks change (March and October).

The Dolphin dial at the Royal Observatory

History of daylight saving time

1784 - Benjamin Franklin first suggested the idea of daylight saving time in a whimsical article.

1907 - An Englishman and keen horse rider, William Willett, campaigned to advance clocks in spring and summer and return them in the autumn. His rather complicated plan was to advance clocks by 80 minutes, in four separate moves of 20 minutes each.

1908 - The House of Commons rejected a Bill to advance the clocks by one hour during the spring and summer months.

1916 - The Summer Time Act was passed, ordaining that for a certain period during the year legal time should be one hour in advance of GMT. Double summer time (GMT + 2 hours) was used during the Second World War.

The history of British Summer Time and daylight saving time