Free tool
Sleep cycle calculator
Enter the time you need to wake up, or the time you plan to go to bed. This sleep calculator works out the other side in full 90-minute sleep cycles, so you wake up closer to the end of a cycle instead of in the middle of one. Nothing you type is stored or sent anywhere.
Ideal bedtimes
Falling asleep takes most people about 14 minutes on average. That buffer is already built into the times above.
This is a general estimate from the standard 90-minute sleep cycle length, not medical advice, and it does not diagnose insomnia, sleep apnea or any other sleep condition. Actual cycle length varies by person and by night. Consult a doctor about ongoing sleep problems.
Sleep cycles and total time asleep
Each full cycle runs about 90 minutes. Waking up at the end of a completed cycle, rather than partway through one, is the idea behind timing sleep in cycles instead of a single round number of hours.
| Sleep cycles | Total time asleep | Typical for |
|---|---|---|
| 3 cycles | 4h 30m | A short night, not a full night’s sleep |
| 4 cycles | 6h 0m | Below the recommended range for most adults |
| 5 cycles | 7h 30m | Lower end of the recommended 7 to 9 hour range |
| 6 cycles | 9h 0m | Upper end of the recommended 7 to 9 hour range |
Common questions
How does this sleep calculator work?
It counts backward or forward in full 90-minute sleep cycles from the time you enter. If you enter a wake-up time, it subtracts 5 and 6 full cycles to suggest two bedtimes, then subtracts another 14 minutes for the average time it takes to fall asleep. If you enter a bedtime, it adds 14 minutes to fall asleep, then adds 5 and 6 full cycles to suggest two wake-up times.
Why 90 minutes for one sleep cycle?
A full sleep cycle, moving through light sleep, deep sleep and REM sleep, takes about 90 minutes on average in adults. Waking up near the end of a completed cycle rather than in the middle of one (especially deep sleep) is commonly linked to feeling less groggy, though the exact length varies from person to person and night to night.
How many hours of sleep do adults actually need?
Most major sleep guidelines put the range for adults at about 7 to 9 hours a night, which works out to roughly 5 to 6 full 90-minute cycles. That is why this tool shows both options rather than a single number: the right one depends on your own schedule and how you feel.
Is this medical advice or a diagnosis of a sleep problem?
No. This tool only does clock arithmetic on a standard, average cycle length. It cannot measure your actual sleep and it does not diagnose insomnia, sleep apnea or any other condition. If you regularly struggle to fall asleep, wake up often, or feel unrested despite enough time in bed, talk to a doctor.
Run a clinic or diagnostic lab?
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- Referring-doctor commission on those follow-up tests is worked out automatically and totalled in one Pay-Run, so nothing is added up by hand.
See how a report reaches the patient on the WhatsApp report delivery page →
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