Calculators
Sleep Calculator
Find the best time to fall asleep or wake up based on 90-minute sleep cycles.
Sleep runs in ~90-minute cycles; waking between cycles feels easier. Times include ~15 minutes to fall asleep.
About this tool
Waking mid-cycle is why 8 hours can still feel awful. Sleep runs in ~90-minute cycles, and waking between cycles feels dramatically easier. Enter your wake-up time to get the ideal moments to fall asleep — or tap "sleeping now" for the best wake-up times.
Times include about 15 minutes to fall asleep. Five to six full cycles (7.5–9 hours) suits most adults.
How to use
- Set your wake-up time (or tap "sleeping now?").
- Pick one of the suggested times — green ones give a full night.
Frequently asked questions
A full sleep cycle through light, deep and REM sleep averages ~90 minutes; waking at a cycle boundary avoids deep-sleep grogginess (sleep inertia).
Most adults do best on 5–6 cycles (7.5–9 hours). Fewer than 4 leaves a sleep debt.
It ranges roughly 80–110 minutes per person — treat the suggestions as good starting points and adjust to how you feel.