Calculate the best bedtime or wake-up time based on 90-minute sleep cycles. Find out when to sleep or wake up to feel fully rested and avoid grogginess.
Assumes ~14 min to fall asleep after you go to bed.
12:56 PM
6 cycles · 9 hours of sleep
2:26 PM
5 cycles · 7.5 hours of sleep
3:56 PM
4 cycles · 6 hours of sleep
5:26 PM
3 cycles · 4.5 hours of sleep
Sleep happens in repeating 90-minute cycles. Each cycle moves through light sleep, deep sleep, and REM (dream) sleep. Waking up at the end of a complete cycle — rather than in the middle — helps you feel alert and refreshed.
Most adults need 5–6 cycles (7.5–9 hours). Waking mid-cycle causes sleep inertia — the groggy feeling you get when an alarm cuts deep sleep short.
Calculate the best time to go to sleep or wake up based on natural 90-minute sleep cycles. Avoid grogginess by timing your alarm to the end of a complete cycle.
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