Waking up in the middle of a sleep cycle can leave you groggy. This free sleep calculator suggests bedtimes or wake-up times based on 90-minute sleep cycles, including a short time to fall asleep.
How it works
A full sleep cycle lasts about 90 minutes on average, moving through lighter and deeper sleep and REM sleep. The calculator counts back (or forward) whole cycles from your chosen time and adds the minutes you usually need to fall asleep. Most adults do best with five or six cycles, which is 7.5 to 9 hours, but needs vary by person.
The 90-minute figure is an average and real cycles vary from night to night. This is a guide, not medical advice. If you often feel tired, talk to a doctor.
Example
To wake at 07:00 with a 15-minute wind-down, five cycles suggests a bedtime of 23:15.
Frequently asked questions
How many hours of sleep do I need?
Many adults need seven to nine hours. Needs vary with age and health.
Are sleep cycles always 90 minutes?
On average, yes, but they vary between people and through the night.
Should I set an alarm for the exact time?
Try it for a week and adjust. Consistent sleep and wake times often matter more than exact minutes.
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This calculator is for general information and is not medical advice.