Sleep Cycle Calculator
Stop waking up groggy. Calculate exactly when to sleep to align with your natural 90-minute REM cycles.
Sleep Cycle Calculator
Wake up refreshed by sleeping in 90-minute REM cycles.
You should try to fall asleep at:
9:45 PM
6 cycles (9 hours of sleep)
Optimal11:15 PM
5 cycles (7.5 hours of sleep)
Optimal12:45 AM
4 cycles (6 hours of sleep)
2:15 AM
3 cycles (4.5 hours of sleep)
* These times include a 15-minute buffer to fall asleep. If you go to bed at these exact times, you should wake up exactly at the end of a sleep cycle!
How to use the Sleep Cycle Calculator
Enter the exact time your alarm is set to go off in the morning.
The tool works backwards in 90-minute REM sleep cycle increments.
It will provide several exact times you should try to fall asleep (with a 15-minute buffer built in) to wake up feeling completely refreshed.
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Open toolFrequently Asked Questions
Why do I feel groggy even after sleeping 8 hours?
Human sleep cycles last approximately 90 minutes. If you wake up in the middle of a deep sleep cycle (e.g. after exactly 8 hours), you will experience sleep inertia (grogginess). Waking up at the end of a cycle (e.g. 7.5 hours or 9 hours) leaves you feeling refreshed.
How many sleep cycles do I need?
Most healthy adults need 5 cycles (7.5 hours) or 6 cycles (9 hours) per night. 4 cycles (6 hours) can be used occasionally, but long-term use leads to sleep deprivation.
Does this calculator account for falling asleep?
Yes! We automatically subtract an extra 15 minutes to account for the average time it takes a human to fall asleep after their head hits the pillow.