Sleep Calculator
Find the best bedtime or wake-up time by sleep cycles.
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About the Sleep Calculator
Work out what time to go to bed — or what time to wake up — free, using 90-minute sleep cycles. Sleep runs in cycles, and waking at the end of one feels dramatically easier than being yanked out of deep sleep mid-cycle. Enter your wake-up time and this sleep calculator counts backwards through 3–6 cycles (plus ~15 minutes to fall asleep) to give you the best bedtimes; or enter when you're going to sleep and get the smartest alarm times. Aim for 5–6 cycles (7.5–9 hours) most nights.
How to use the Sleep Calculator
- 01Choose whether you're setting a wake-up time or a bedtime.
- 02Enter the time.
- 03Pick one of the suggested times — each lands at the end of a sleep cycle.
Frequently asked questions
Why 90-minute cycles?
A full sleep cycle — light, deep, and REM sleep — averages about 90 minutes. Waking between cycles leaves you clearer-headed than waking mid-cycle.
How many sleep cycles do I need?
Adults do best with 5–6 cycles (7.5–9 hours). Four cycles (6 hours) works occasionally, but not as a routine.
Why do I feel groggy after 8 hours?
You likely woke mid-cycle. Timing sleep in 90-minute multiples — 7.5 or 9 hours instead of 8 — often beats simply sleeping longer.