It happens every single year, but somehow we still struggle to remember when we're supposed to move our clocks back by an hour.
And the question on everyone's mind is whether we'll be losing or gaining some extra precious minutes of sleep.
The change in time this month will take us from British Summer Time (BST) back to Greenwich Mean Time (GMT).
While your phone automatically gets the memo, any analogue clocks and those pesky ones on your oven may need a little help.
So, why do we change the clocks every year and when will it happen?
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When do clocks go back in October 2021?
Clocks will be going back by an hour on the final Sunday of October at 2am, so this year it'll be on Sunday, October 31.
This means everyone will be gaining an extra hour of sleep, so you may wake up with a fright on Halloween when it feels later than it actually is.
The clocks will remain in the GMT time zone until spring, which is when BST will return and the clocks will go forward by an hour again.
However, that is some way off - the clocks will not be going forward again until Sunday, March 27, 2022 at 1am. This is because the BST change takes place at 1am on the final Sunday in March.
If you're confused about which way the clocks change through the seasons, remember the classic saying "spring forward, fall backwards" to help you.
Why do we change the clocks?
The clocks are changed in order to make the most of daylight hours in the UK, and by moving the clocks back by an hour in autumn we get an extra hour of it.
And, when we switch to BST, it allows us to get more daylight again, but in the evening.
British Summer Time was introduced in the early 20th century as builder William Willet despaired at the waste of daylight during summer and the system has changed several times over the years.
In the seventies, Britain went back to the system we currently use whereby the clocks alter in spring and autumn.
The reason for the clocks being changed on Sundays is because it is the weekend, when many people are off work and school, which allows for people to adjust and prevents disruption.
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