Sleep Calculator
How to use the sleep calculator
- Choose whether you know when you want to wake up or when you go to bed, and enter the time. Now fills in the current time for going to bed now.
- Set how long you usually take to fall asleep; about 15 minutes is typical.
- Pick one of the times shown. The highlighted ones give 5 or 6 full cycles, 7.5 or 9 hours of sleep.
Frequently asked questions
Why 90-minute cycles?
Sleep runs in cycles of light, deep and REM sleep that last about 90 minutes on average, though they vary from about 70 to 120 minutes. Waking at the end of a cycle, rather than out of deep sleep, tends to leave you less groggy.
How much sleep do adults need?
At least 7 hours a night, according to the American Academy of Sleep Medicine and the Sleep Research Society: 5 cycles. Teenagers need 8 to 10 hours.
Are the times exact?
No. Your own cycles are longer or shorter than 90 minutes and change through the night, so take the times as a guide and move them by 10 to 15 minutes if you still wake up tired.