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Sleep Cycle Calculator

Find bedtimes or wake-up times that align with complete 90-minute sleep cycles, from either end of the night.

Wake up at (3 cycles, 4h 30m sleep)
3:45 AM
Wake up at (4 cycles, 6h sleep)
5:15 AM
Wake up at (5 cycles, 7h 30m sleep)
6:45 AM
Wake up at (6 cycles, 9h sleep)
8:15 AM

How it works

Sleep runs in cycles that average about 90 minutes each, moving through lighter and deeper stages before starting over — waking near the boundary between two cycles is commonly reported as easier than waking in the middle of one, which is the idea behind every calculator of this kind. This one just does the clock arithmetic: it adds your fall-asleep buffer, then lays out 3, 4, 5, and 6 complete 90-minute cycles (4.5 to 9 hours of sleep) from whichever anchor time you enter.

If you enter a bedtime, each recommended time is bedtime + fall-asleep buffer + (cycles × 90 minutes), wrapped to the next day past midnight. If you enter a wake-up time instead, each recommended bedtime is wake time − (cycles × 90 minutes) − fall-asleep buffer, wrapped backward past midnight the same way.

This models the cycle-length arithmetic only — it isn't a claim about how many hours of sleep is right for you, which varies by person and isn't something a formula can determine from a clock time alone.

FAQ

Why 90 minutes specifically?

90 minutes is the commonly cited average length of one full sleep cycle in adults, though an individual's actual cycles can run somewhat shorter or longer and even vary night to night. It's a useful planning average, not a measurement of your own sleep.

Why does the calculator ask how long it takes you to fall asleep?

Your sleep cycles only start once you're actually asleep, not the moment you get into bed. Skipping this buffer (or leaving it at 0 if you fall asleep almost instantly) would shift every recommended time earlier than when your first cycle really begins.

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