This is a rough guide, not medical advice. If you sleep too much or too little, talk to a doctor.
How to use it
This page explains how the bedtimes and wake-up times are worked out.
- Choose whether you know your wake-up time or your bedtime.
- Enter the time. The result shows 6, 5 and 4 cycles.
- Under “Adjust”, set how long you take to fall asleep, the cycle length and your age group.
How it works
- During the night you go through cycles of non-REM and REM sleep. The NHLBI says a cycle starts over every 80 to 100 minutes, with 4 to 6 cycles a night, and you may wake briefly between them.
- Bedtime = wake-up time − cycles × cycle length − time to fall asleep. Wake-up time works the same way forward.
- The big time is the shortest option within the recommended hours for your age group.
- Time to fall asleep starts at 15 minutes. We found no official average, so set your own.
Sources and date checked
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Frequently asked questions
- How long is a sleep cycle?
- About 80 to 100 minutes, according to the NHLBI at the US National Institutes of Health. Most nights have 4 to 6 cycles. This calculator uses 90 minutes unless you change it.
- What time should I go to bed to wake up at 7 AM?
- With 90-minute cycles and 15 minutes to fall asleep: 9:45 PM for 6 cycles (9 hours) or 11:15 PM for 5 cycles (7.5 hours). Adults are advised to sleep 7 to 9 hours.
- How much sleep do I need?
- The NHLBI says adults need 7 to 9 hours a night, teens 8 to 10 hours and children 6 to 12 years 9 to 12 hours, naps included.
Notes and your data
- Nothing you enter is saved or sent anywhere. The calculation runs in this browser.
- Real cycles vary by person and by night. The times are a starting point, not a prescription.
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