Sleep calculator
Find the best time to go to bed or wake up, based on 90-minute sleep cycles.
About this calculator
Choose whether you know when you need to wake up or when you are going to bed, and the calculator counts back or forward in 90-minute sleep cycles, allowing time to fall asleep.
Five to six cycles, about 7.5 to 9 hours, suit most adults. This is a guide and not medical advice.
Measurements and terms explained
- Sleep cycle
- A repeating pattern of light sleep, deep sleep and REM sleep, about 90 minutes long.
- Time to fall asleep
- How long it usually takes you to drift off after getting into bed. 10 to 20 minutes is common.
Common questions
How much sleep do I need?
Most adults need 7 to 9 hours. Children and teenagers need more.
Why 90 minutes?
A full cycle of light, deep and REM sleep lasts roughly 90 minutes, although it varies between people.
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