Sleep Cycle Calculator
Sleep happens in roughly 90-minute cycles. Pick whether you're planning a wake time or a bedtime to find times that align with a full cycle.
FAQ
Why 90-minute cycles?
Sleep moves through repeating cycles of roughly 90 minutes each, moving through light sleep, deep sleep, and REM sleep. Waking up at the end of a cycle, rather than in the middle of deep sleep, generally feels less groggy.
How many cycles should I aim for?
Most adults benefit from 5-6 full cycles per night, which works out to roughly 7.5-9 hours of sleep. This calculator shows options across that range so you can pick what fits your schedule.
Does this account for falling asleep time?
Yes — the calculator adds roughly 15 minutes to account for the average time it takes to actually fall asleep after getting into bed, so the suggested times are more realistic.
Is 90 minutes exact for everyone?
No — actual cycle length varies somewhat by individual, typically between 80-120 minutes. This calculator uses the commonly cited 90-minute average as a useful general guide, not an exact personal measurement.
About this tool
This calculator works backward or forward from a target wake-up or bedtime, showing options that align with full 90-minute sleep cycles. Waking at the end of a cycle rather than mid-cycle can help you feel less groggy. This is a general guide, not medical advice.