Sleep calculator

Sleep calculator

Find a bedtime that fits your sleep cycles

Enter the time you need to wake up and how long you usually take to fall asleep. The calculator suggests bedtimes that give you 6, 5 or 4 full sleep cycles of about 90 minutes, so you're more likely to wake at the end of a cycle rather than in the middle of one.

How the bedtimes are worked out

During the night you go through several cycles of lighter and deeper sleep. A cycle lasts about 90 minutes on average. Waking at the end of a cycle, when sleep is lighter, can leave you feeling less groggy than waking from deep sleep.

The calculator counts back from your wake-up time: bedtime = wake-up time − number of cycles × 90 minutes − the time it takes you to fall asleep. Six cycles is 9 hours' sleep, five is 7.5 hours and four is 6 hours.

Worked example

If you need to wake at 07:00 and take 15 minutes to fall asleep, go to bed at 22:45 for 6 cycles (9 hours), 23:15 for 5 cycles (7.5 hours) or 00:45 for 4 cycles (6 hours).

Treat the times as a guide

Sleep cycles vary between people and through the night, and you may wake briefly between them. So the 90-minute figure is an average, not a precise timer.

Six hours is shown as a shorter option, but regularly sleeping that little can leave you tired. Going to bed and getting up at the same times each day usually matters more than hitting an exact cycle.

This isn't medical advice. If you often struggle to sleep or feel tired despite enough sleep, talk to your GP.

Inputs for the sleep calculator

Time you need to wake up

The time your alarm goes off, in 24-hour format.

Time it takes you to fall asleep

How many minutes it usually takes you to drop off after getting into bed, from 0 to 120.

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