Sleep Calculator (Sleep Cycle Calculator)
Enter the time you want to wake up to see when to go to bed, or enter the time you plan to sleep (or tap "Sleep now (current time)") to see when to wake up. The results are based on roughly 90-minute sleep cycles and your time to fall asleep (15 minutes by default), and list options for 4 to 6 cycles (6 to 9 hours). Everything is calculated in your browser, and nothing you enter is sent to a server. Need to work out an age or a date difference? Try the Age Calculator.
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A whole number from 0 to 120. How long it usually takes you to drift off after lying down.
Notes
- The 90-minute cycle is a rule of thumb. Real cycles vary by person and by night, typically from about 80 to 110 minutes.
- Results are not a medical diagnosis or personal health advice. If you have ongoing insomnia or heavy daytime sleepiness, talk to a doctor.
- Times use the 24-hour clock. When a result falls on another day, it is labeled "previous day" or "next day".
Glossary
Sleep cycle
One full pass through non-REM and REM sleep, lasting about 90 minutes in adults. A night usually contains four to six of them.
Sleep latency
The time between lying down and actually falling asleep. You can set it as "Time to fall asleep"; the default is 15 minutes.
FAQ
Why does the calculator use 90-minute blocks?
A sleep cycle, one pass through non-REM and REM sleep, lasts about 90 minutes in adults. Waking at the end of a cycle is thought to feel easier, but the real length varies from person to person.
What should I enter for the time to fall asleep?
Enter how long it usually takes you to fall asleep after getting into bed. The default is 15 minutes. Use a lower number if you drift off quickly and a higher one if you need longer.
How are times that cross midnight shown?
Times use the 24-hour clock, with "previous day" or "next day" added when the result is on a different day than the time you entered. For a 07:00 wake-up, 23:15 is the evening before.
Will I definitely wake up refreshed if I follow the result?
There is no guarantee. Sleep quality also depends on your health, environment and accumulated sleep debt. The results are estimates, not medical advice.
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