Health & Wellness
Sleep Cycle Calculator
Calculate the best bedtime or wake-up time based on 90-minute REM sleep cycles. Wake up refreshed, avoid sleep inertia, and optimize deep restorative rest.
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Optimal Times to Wake Up Refreshed:
8:14 AM
6 cycles (9.0 hrs)
6:44 AM
5 cycles (7.5 hrs)
★ Recommended
5:14 AM
4 cycles (6.0 hrs)
3:44 AM
3 cycles (4.5 hrs)
Frequently Asked Questions
How long is a human sleep cycle?
A complete sleep cycle lasts roughly 90 minutes, cycling through light sleep, deep slow-wave sleep, and REM dreaming sleep.
Why is waking up at the end of a cycle important?
Waking up mid-cycle from deep sleep triggers "sleep inertia", leaving you groggy. Waking at the end of a 90-minute cycle feels natural and alert.