Sleep Calculator
Find the best times to go to bed or wake up, based on 90-minute sleep cycles.
Go to bed at one of these times
Assumes about 15 minutes to fall asleep.
How it works
Sleep happens in cycles of about 90 minutes. Waking up at the end of a cycle — rather than in the middle — helps you feel more rested. This tool suggests times for 4, 5 or 6 full cycles (6 h, 7 h 30 or 9 h), plus ~15 minutes to fall asleep.
How it works
Sleep runs in cycles of roughly 90 minutes, moving from light sleep to deep sleep and REM and back. Waking at the end of a cycle — rather than in the middle of deep sleep — is what leaves you feeling refreshed rather than groggy. This calculator works backwards or forwards in 90-minute blocks. Tell it when you want to wake up and it suggests bedtimes that land on a cycle boundary; tell it when you're going to bed and it suggests good wake-up times. It also adds about 15 minutes for the time it takes to fall asleep. Most adults need five to six full cycles (about 7.5 to 9 hours) a night. Use the suggested times as targets, and adjust to how you actually feel — cycle length varies from person to person.
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Frequently asked questions
Why 90-minute cycles?
A full sleep cycle (light, deep and REM sleep) lasts about 90 minutes. Waking at the end of one, not in the middle, reduces grogginess.
How many cycles do I need?
Most adults feel best with 5 to 6 cycles per night (about 7.5 to 9 hours).
How long is one sleep cycle?
About 90 minutes on average, though it ranges from roughly 70 to 120 minutes and varies between people and across the night.
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