Sleep Calculator
When to go to bed so you wake up at the end of a sleep cycle rather than in the middle of one, or when to set your alarm if you go to sleep now.
Last updated
How to work out the best time to sleep
- Choose I want to wake up at…, I’m going to bed at… or I’m going to sleep now.
- Enter the time, and adjust how long you take to fall asleep if 15 minutes isn’t right for you.
- Pick one of the suggested times, which line up with the end of a sleep cycle.
How it works
Sleep runs in cycles of roughly 90 minutes (anywhere from about 80 to 110, and different through the night), each passing from light sleep into deep sleep and then REM sleep. Waking at the end of a cycle, when sleep is lightest, usually feels easier than being pulled out of deep sleep partway through, which causes the groggy feeling called sleep inertia. The calculator counts whole cycles back from your alarm, or forward from your bedtime, after allowing for the time it takes you to drift off (15 minutes is typical).
Five or six cycles (7½ to 9 hours) suits most adults; the NHS and sleep scientists recommend 7 to 9 hours for adults, 8 to 10 for teenagers and 9 to 12 for school-age children, so the suggestions are marked accordingly. If you often wake just before your alarm, your cycles may be a little shorter: try 85. Cycle timing is an average, not a guarantee, and this isn't medical advice. If you're regularly tired despite enough sleep, talk to your GP.
| Age | Recommended sleep per day |
|---|---|
| Babies 4–12 months | 12–16 hours, including naps |
| 1–2 years | 11–14 hours, including naps |
| 3–5 years | 10–13 hours, including naps |
| 6–12 years | 9–12 hours |
| 13–18 years | 8–10 hours |
| Adults | 7–9 hours |
Questions about sleep cycles
What time should I go to bed to wake up at 7am?
For five or six 90-minute cycles plus 15 minutes to fall asleep, aim for 21:45 or 23:15. Enter 07:00 to see all the options.
How long is a sleep cycle?
About 90 minutes on average, though it varies from roughly 80 to 110 minutes between people and through the night.
How much sleep do adults need?
The NHS recommends 7 to 9 hours for adults, 8 to 10 for teenagers and 9 to 12 for children aged 6 to 12.
Why do I feel groggy even after a long sleep?
Waking in the middle of deep sleep causes grogginess called sleep inertia. Waking at the end of a cycle usually feels easier. If you’re always tired, talk to your GP.