Sleep Cycle Calculator

Frequently asked

Q. Why a 90-minute sleep cycle?

A. Sleep medicine treats one N1→N2→N3 (deep)→REM cycle as 90 min on average. Early cycles run shorter and late ones lengthen as REM grows, producing 80–110 min variance — the tool lets you tune 85–105 min.

Q. Is 6 h (4 cycles) or 7.5 h (5 cycles) better?

A. Adults need 7–9 h, so 5–6 cycles is the safe zone. Four cycles works short-term but accumulates cognitive, immune, and metabolic costs. 5–6 cycles are highlighted as recommended.

Q. How should I set the sleep-onset value?

A. Healthy adults fall asleep in 10–20 min; the default is 14 min. Tune to 5–10 min if you fall asleep fast, 20–30 min if slow. Under 5 min may signal sleep deprivation; recurring 30 min+ may indicate insomnia.

Q. Can this be used for medical diagnosis or treatment?

A. No. This is a reference calculator built on population averages, not a medical device. Persistent insomnia, excessive daytime sleepiness, or suspected sleep apnea require a clinic visit.

Q. Does it integrate with Apple Health or Fitbit?

A. No. Apple Health®, Fitbit®, Oura® are registered trademarks of their owners; this is an unaffiliated calculator that performs simple time math without ingesting external data.