Sleep Calculator
Waking up in the middle of a sleep cycle makes you groggy. Tell us when you need to wake up, or when you are going to bed, and get times that line up with complete sleep cycles.
Free · No sign-up · Files stay on your device
How to use Sleep Calculator
- 1Choose "I need to wake up at" or "I am going to bed at".
- 2Enter the time.
- 3Pick one of the suggested times (5–6 cycles is ideal for adults).
Features
- Bedtimes for a wake-up time
- Wake-up times for a bedtime
- "Sleep now" option
- Adjustable time to fall asleep
- 12- or 24-hour times
Why 90-minute cycles?
Sleep moves through light, deep and REM stages in cycles of roughly 90 minutes. Waking at the end of a cycle, when sleep is lightest, feels easier. Most adults need 5 or 6 cycles (7.5–9 hours). The calculator also adds the average 15 minutes it takes to fall asleep.
Frequently asked questions
How much sleep do I need?
Adults generally need 7–9 hours, teenagers 8–10, and school-age children 9–12.
Are cycles always 90 minutes?
They range from about 80 to 110 minutes and vary by person and through the night, so treat the times as a guide.
What if I take longer to fall asleep?
Change the "Time to fall asleep" setting.
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