Sleep Cycle Calculator
Waking between cycles matters more than total hours.
Reading your result
Fill in every field and the steps will be spelled out here.
How it is calculated
Sleep moves through roughly 90-minute cycles of lighter and deeper stages. Waking at the end of one feels clean; an alarm in the middle of deep sleep leaves you groggy even after more total hours. That is why six hours occasionally beats seven.
Falling asleep has to be in the arithmetic. Almost nobody drops off the moment they lie down — around 14 minutes is typical for adults — so a 7am wake with six cycles means lights out at 1:32, not 1:46. This calculator subtracts it for you.
Ninety minutes is an average, not a constant. It runs anywhere from 80 to 110 minutes between people and drifts across the night in any one person. Treat the times below as a neighbourhood to aim for rather than a schedule to hit to the minute.
Trimming cycles buys time only briefly. Four cycles will carry you a night or two, but the deficit accumulates in reaction time and judgement, and weekend catch-up sleep does not fully repay it.
Frequently asked questions
Is 90 minutes exact?
It is an average. Individual cycles run 80–110 minutes, and REM takes up more of each cycle as the night goes on. Use it as an approximate target rather than a precise schedule.
Six hours or seven?
On cycle logic, six hours (four cycles) can feel better than seven (about 4.7 cycles), because seven lands mid-cycle. Cumulative sleep debt is a separate matter, though — over time 7.5 hours, five cycles, is the better target.
How long should a nap be?
Either under 20 minutes or a full 90. The 30–60 minute range wakes you out of deep sleep, which is why it often leaves you heavier than before.
Sleep cycles vary widely between individuals and shift with age, sleep debt, medication and caffeine. This is a general guide — persistent insomnia or daytime sleepiness is worth discussing with a clinician.