Sleep Cycle Calculator
Work out the best times to wake up based on 90-minute sleep cycles, either from a bedtime or working backward from a wake-up time.
Frequently asked questions
Is this tool free?
Yes. Calchemy tools are free to use in your browser.
Is my data uploaded?
No. The tools are designed to run locally in your browser unless clearly stated otherwise.
Why 90-minute cycles?
Sleep moves through cycles of roughly 90 minutes each, and waking up near the end of a cycle (in lighter sleep) generally feels easier than waking mid-cycle during deep sleep. This is a widely used approximation, not an exact figure - actual cycle length varies by person and by night.
What's the 14 minutes for?
It's a typical estimate of how long it takes to actually fall asleep after getting into bed, added on so the cycle counts line up with real wake-up times rather than assuming instant sleep.
Is this a substitute for good sleep habits?
No. This is a rough planning guide, not medical advice. Consistent sleep and wake times, avoiding late caffeine, and getting enough total sleep matter far more than hitting an exact cycle boundary. See a doctor if you have ongoing sleep problems.