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Sleep Calculator
Free online sleep calculator. Find the best bedtime or wake-up time based on 90-minute sleep cycles.
Recommended Times
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Wake up refreshed by timing your sleep in 90-minute cycles. The human sleep cycle lasts about 90 minutes — waking up at the end of a cycle means you feel alert, not groggy.
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FREQUENTLY ASKED QUESTIONS
How many sleep cycles do I need?
Most adults need 5-6 complete sleep cycles per night, which equals 7.5-9 hours of sleep.
What is a sleep cycle?
A sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM sleep stages. Waking mid-cycle causes grogginess.
Is it better to sleep less or wake mid-cycle?
It is often better to sleep slightly less and wake at the end of a cycle than to sleep longer but wake in the middle of deep sleep.
How long should a nap be?
A 20-minute power nap avoids deep sleep and leaves you alert. A 90-minute nap completes one full cycle and is also effective.