On the last Sunday of October in the UK, the clocks go back by one hour.

It may feel like a long time since the blue skies of summer, but the moment when the clocks go back marks the end of British Summer Time (BST). Good news: it also means an extra hour in bed.

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

Most devices with internet connection, such as smartphones, computers and other digital devices should automatically update.

Some watches and clocks in cars and kitchens for example may not change on their own however, 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," she says.

"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 use of different dial rims for Greenwich Mean Time and British Summer Time, and of the two different hour-plates with the hour lines marked, means that the Dolphin sundial at the Royal Observatory is accurate whatever the time of year.

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.

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 5 November 2023.

In March 2019, the European Parliament backed a proposal to end the practice of changing the clocks in European Union states. The proposal was originally meant to be introduced in 2021, but the amendment has not taken legal effect. EU states continue to use daylight saving time.