Sleep Cycle Calculator
When should you go to bed to wake up refreshed? Get bedtimes that finish full 90-minute sleep cycles in seconds.
Advanced: sleep cycle length
Most people average about 90 minutes. Leave it at 90 unless you know yours is different.
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What is a sleep cycle, and why 90 minutes?
During the night your brain moves through repeating sleep cycles — light sleep, then deep sleep, then REM (dreaming) — before starting over. One full cycle lasts about 90 minutes on average, so a good night is usually made of several complete cycles rather than a fixed number of hours.
How many sleep cycles or hours of sleep do I need?
Most adults feel best on 5 to 6 full cycles a night, which is roughly 7.5 to 9 hours of sleep. This sleep cycle calculator highlights the 5- and 6-cycle options as recommended, and still shows shorter 3- to 4-cycle plans for the nights when you simply can't get a full rest.
Why is it better to wake up at the end of a cycle?
Waking in the middle of deep sleep triggers sleep inertia — that heavy, groggy feeling that can linger for a while. If your alarm lands at the end of a cycle, when sleep is lightest, you tend to wake up more easily and feel refreshed, even after the same amount of sleep.
Why does the calculator add about 15 minutes to fall asleep?
Almost nobody falls asleep the instant their head hits the pillow. This gap is called sleep latency, and it shifts your real bedtime. The bedtime calculator adds your fall-asleep time (15 minutes by default, adjustable from 0 to 60) so the cycles are counted from when you actually drift off, not from when you get into bed.
Is this medical advice, and is my sleep data private?
No — the times here are averages meant for general reference, not medical advice; if you have ongoing sleep problems, talk to a doctor. Your privacy is fully protected: every calculation runs inside your browser, your times are saved only on your own device, and nothing is ever sent to a server.