Sleep Cycle
Calculator
Sleep runs in roughly 90-minute cycles. Waking at the end of one — rather than mid-cycle — tends to feel less groggy. Work backward from your alarm, or forward from now.
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Best bedtimes
How this works
Methodology reviewed July 2026Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle — rather than mid-cycle, in deep sleep — tends to feel less groggy. Given a wake time or a bedtime, the tool counts back or forward in 90-minute blocks (plus a short allowance for falling asleep) to suggest times that land on cycle boundaries.
bedtime = wake time − (n × 90 min) − ~15 min to fall asleep
wake time = bedtime + (n × 90 min) + ~15 min to fall asleep
(n = whole sleep cycles, typically 4–6)
A target bedtime or wake time · Optional time-to-fall-asleep
Suggested wake or bed times aligned to 90-minute cycles
- A 90-minute average cycle and ~15 minutes to fall asleep — both vary night to night and person to person.
- Cycle length isn't exactly 90 minutes and drifts across the night, so these are approximations.
- Total sleep duration and consistency matter far more than hitting an exact cycle boundary.
- Persistent poor sleep or suspected sleep disorders deserve a clinician, not a timing tweak.
This calculator is for educational purposes only and is not medical advice, diagnosis, or treatment. Results are estimates based on published formulas and population averages — your individual values may differ. Nothing here is calculated on a server: everything runs in your browser and no data is stored or sent anywhere. Always consult a qualified clinician before making health, medication, or training decisions.