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Sleep Calculator
Find the best bedtime or wake-up time based on 90-minute sleep cycles.
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6 sleep cycles.
| 5 cycles (7.5 h) | — |
|---|---|
| 4 cycles (6 h) | — |
| 6 cycles (9 h) | — |
| Note | — |
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Enter your figures above to see the step-by-step working.
An estimate — cycles varyEverything computed client-side — nothing leaves this page
How the Sleep Calculator Works
Sleep moves through cycles of about 90 minutes, and waking at the end of a cycle — rather than mid-cycle — leaves you feeling far more refreshed. This calculator counts back (or forward) in 90-minute cycles, adding about 14 minutes to fall asleep, to suggest bedtimes for a chosen wake-up time, or wake times if you’re going to bed now.
Most adults do best on 5 to 6 cycles a night (7.5 to 9 hours). The times are estimates — cycle length varies from person to person and night to night — but aligning sleep to whole cycles is a simple way to wake up less groggy.
bedtime = wake time − (cycles × 90 min + 14 min to fall asleep)
Frequently Asked Questions
What time should I go to bed to wake at 7am?
Counting back whole 90-minute sleep cycles plus time to fall asleep, good bedtimes are around 9:46 PM (6 cycles) or 11:16 PM (5 cycles).
Why 90-minute cycles?
A full sleep cycle averages about 90 minutes. Waking at the end of one, rather than in deep sleep, leaves you feeling more rested.
How many hours of sleep do I need?
Most adults need 7 to 9 hours — about 5 to 6 sleep cycles. Children and teens need more.
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