Sleep Calculator
Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle feels far easier than being pulled out of the middle of one. Tell the calculator when you need to get up, or when you are going to bed, and it finds the times that line up.
Type a number and the answer appears straight away.
To wake at 7:00 AM, go to bed at11:15 PM5 sleep cycles, 7.5 hours of sleep
- For 6 cycles (9 hours)
- 9:45 PM
- For 4 cycles (6 hours)
- 12:45 AM
Based on 90-minute sleep cycles, which is an average: real cycles run from about 70 to 120 minutes. Adults are advised to sleep at least 7 hours a night.
| Sleep cycles | Time asleep | Go to bed at |
|---|---|---|
| 6 | 9 hours | 9:45 PM |
| 5 | 7.5 hours | 11:15 PM |
| 4 | 6 hours | 12:45 AM |
| 3 | 4.5 hours | 2:15 AM |
The math behind it: Sleep Cycle
bedtime = wake-up time - (cycles x 90 minutes) - time to fall asleep
To wake at 7:00 AM after five full cycles, allowing 15 minutes to fall asleep, go to bed at 11:15 PM. For six cycles and nine hours of sleep, make it 9:45 PM. Ninety minutes is an average: real cycles run from about 70 to 120 minutes, so use the times as a guide.
Common questions
What time should I go to bed if I wake up at 7 AM?
At 11:15 PM for five sleep cycles (7.5 hours of sleep), or 9:45 PM for six cycles (9 hours). Both allow 15 minutes to fall asleep.
How long is a sleep cycle?
About 90 minutes on average. Each cycle moves through light sleep, deep sleep and REM sleep. Most adults go through four to six cycles a night.
How many hours of sleep do I need?
Adults are advised to get at least 7 hours a night. Teenagers need 8 to 10 hours and school-age children 9 to 12.
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