Sleep calculator●
Pick a wake-up time and see when to go to bed, or the other way round, using 90 minute sleep cycles.
The result updates as you type. Nothing you enter leaves this page.
Uses the current time on your device. The wake-up times refresh while this page is open.
Sleep times
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The times you enter are used only in this browser tab. Nothing is sent, saved or tracked.
How sleep cycles work
During the night you move through sleep in cycles of about 90 minutes, from light sleep to deep sleep to dream sleep. Waking up at the end of a cycle usually feels easier than being pulled out of deep sleep, even when the total time is the same. This calculator counts backwards from your wake-up time, or forwards from your bedtime, in whole cycles and adds the minutes you need to fall asleep. Three cycles is 4.5 hours, four is 6 hours, five is 7.5 hours and six is 9 hours. Cycle length varies from person to person and from night to night, so treat the times as a good starting point and adjust them to how you feel.
Time calculator →Common questions
How long is a sleep cycle?
About 90 minutes on average. It can range from roughly 80 to 110 minutes and changes during the night.
How many hours of sleep do I need?
Most adults do well on 7 to 9 hours, which is 5 or 6 cycles. Needs differ by age and person, and children and teenagers need more.
Why does the calculator add 15 minutes?
It is the time many people take to fall asleep. You can change it from 0 to 45 minutes to match your own habit.
Is this medical advice?
No. It is a general guide based on average sleep cycles. If you often feel unrested or have trouble sleeping, talk to a doctor.
Is anything sent anywhere?
No. The calculation runs in your browser.