Sleep Calculator
Compute ideal sleep bedtimes counting back in 90-minute cycles — whole and half-cycle rows (2 to 5 cycles) minus a 15-minute buffer. Wake refreshed at cycle ends, not mid-dream — free, local, no signup.
How to Use the Sleep Calculator
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Frequently Asked Questions
Why 90-minute cycles?
Sleep runs ~90-minute REM/non-REM loops; waking at cycle ends avoids grogginess. Count back in 90s from alarm plus 15 min to fall asleep.
How many cycles?
The tool lists 2 to 5 cycles in half-cycle steps (2, 2.5, 3, 3.5, 4, 4.5, 5 — i.e. 3–7.5 hours), each 90 minutes times cycles plus a 15-minute buffer: a 06:30 alarm with 5 cycles means a 22:45 bedtime. Prefer whole-cycle rows; half-cycle rows split a 90-minute loop.
Are naps included?
20 minutes (no deep sleep) or 90 full cycles — 40–60 minute naps wake mid-cycle groggy. Time naps deliberately.
Do bedtime math upload?
No — math runs locally in your browser. Nothing leaves your device.
Last updated October 2026