Free Sleep Cycle Calculator

Find the best times to go to bed or wake up, based on 90-minute sleep cycles and the time it takes to fall asleep.

Go to bed at one of these times
9:45 PM
6 cycles · 9h
Recommended
11:15 PM
5 cycles · 7.5h
Recommended
12:45 AM
4 cycles · 6h
2:15 AM
3 cycles · 4.5h

Based on 90-minute sleep cycles plus about 15 minutes to fall asleep. Cycle length varies from person to person and night to night, so treat these as a helpful guide.

How to use / FAQ

Enter the time you need to wake up and the calculator works backward in 90-minute sleep cycles to suggest the best bedtimes — or pick 'if I sleep now' to see the best times to wake up. Everything runs in your browser; nothing is stored.

How does the sleep cycle calculator work?

Sleep moves through cycles of roughly 90 minutes. Waking at the end of a cycle, rather than in the middle of deep sleep, tends to leave you feeling more refreshed. The tool counts whole 90-minute cycles back from your wake time (or forward from now) and adds about 15 minutes for the time it takes to fall asleep.

How many sleep cycles do I need?

Most adults do well with five to six cycles a night — about 7.5 to 9 hours. The tool highlights the five- and six-cycle options as recommended, but shows four- and three-cycle times too for shorter nights or naps.

Why add 15 minutes to fall asleep?

Very few people fall asleep the instant their head hits the pillow. A short buffer makes the suggested bedtimes more realistic so your cycles line up with your alarm. If you fall asleep faster or slower, adjust the times a little.

Are 90-minute cycles exact?

No. Ninety minutes is a widely used average, but real cycles range from about 70 to 120 minutes and change through the night and from person to person. Treat these times as a helpful starting point rather than a precise schedule.