Sleep Cycle Calculator

Sleep happens in cycles of roughly 90 minutes, and waking up at the END of a cycle (rather than in the middle of one) tends to feel far less groggy. This calculator works backward or forward from a target time in whole 90-minute cycles, plus about 15 minutes to actually fall asleep.

7.5 hours (5 cycles)
11:15 PM
The most commonly recommended amount
9 hours (6 cycles)
9:45 PM
6 hours (4 cycles)
12:45 AM

How it works

If you want to wake up at a certain time, the calculator subtracts whole 90-minute cycles (plus a 15-minute buffer to fall asleep) to suggest bedtimes. If you're going to bed at a certain time, it adds cycles forward to suggest wake-up times.

Formula
Bedtime = wake time - (cycles x 90 + 15) minutes | Wake time = bedtime + 15 + (cycles x 90) minutes

Example. To wake up at 7:00 AM, going to bed at 11:15 PM gives 5 full cycles (7.5 hours) of sleep.

Why cycles matter more than just hours

Waking up mid-cycle - during deep sleep, for example - is what makes an alarm feel especially jarring even after 7-8 hours in bed. Timing your wake-up to land between cycles, at a whole multiple of about 90 minutes, tends to feel noticeably more refreshed even at a similar total sleep duration.

Frequently asked questions

Is 90 minutes an exact number for everyone?

No - it's a useful average. Individual sleep cycles typically range from about 70 to 120 minutes and can vary night to night. Treat these times as a good starting estimate to experiment with, not an exact science.

How many cycles should I aim for?

5 cycles (7.5 hours) is a common sweet spot for adults, but individual needs vary - some people feel best on 6 cycles (9 hours), especially when younger or more physically active.

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