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Sleep Calculator

This calculator plans your bedtime or your wake time around complete 90-minute sleep cycles. Waking at the end of a cycle tends to feel sharper than being pulled out of the middle of one.

The Sleep Calculator is only an estimate. Cycle length varies from person to person and from night to night, and is affected by age, stress, alcohol, caffeine, shift work, and health conditions, so the times shown are a starting point rather than a precise schedule. The calculator should not be used as a sole diagnostic tool.

Ongoing trouble falling asleep, staying asleep, or feeling rested is worth raising with a licensed healthcare provider, as it can point to a treatable sleep disorder. This calculator is not a substitute for that consultation.


Why 90-minute cycles?


A full sleep cycle — light → deep → REM — runs around 90 minutes for most adults. Waking at the end of a cycle feels sharper than being jolted mid-cycle. The multiples we show target cycle boundaries.

How much sleep do I really need?


Adults 18–64 need 7–9 hours (5–6 cycles). Teenagers 8–10 hours (5–7 cycles). Seniors 65+ 7–8 hours (5 cycles). Under 7 hours is associated with worse health outcomes across the board.

What about sleep latency?


Sleep latency is the time from lights-off to actually being asleep — usually 10–20 minutes. We subtract it from your target bedtime so the math works out to real wake-up feelings.

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