Free calculator
Sleep Cycle Calculator
Sleep runs in cycles of about 90 minutes. Waking at the end of one, rather than in the middle, usually feels easier.
How it works
Bedtime = wake time − (cycles × 90 minutes) − time to fall asleep. Adults need 7–9 hours, so 5 or 6 cycles (7.5 or 9 hours) are the ideal choices; 4 cycles (6 hours) is the minimum we show.
Cycle length varies from 70 to 110 minutes between people and through the night, so use the times as a starting point.
Frequently asked questions
What if I wake in the night?
It is normal. Avoid checking the time and keep lights dim.
Do naps follow cycles?
A 20-minute nap or a full 90-minute nap avoids deep-sleep grogginess.
How does light affect sleep?
Bright light in the evening delays sleep; morning daylight helps anchor your clock.
General estimates for information only. Not medical or professional advice. Nothing you enter is saved or sent to us.