Sleep cycle calculator

How to use this tool

1. Choose whether you want to find a bedtime for a wake-up time, or a wake-up time for a bedtime.
2. Enter the time and how long you usually take to fall asleep.
3. Read the suggested times that line up with 90-minute sleep cycles.
4. Pick the one that fits your day and set your alarm.

How it works

Sleep runs in cycles of roughly 90 minutes, from light sleep to deep sleep to dreaming. Waking at the end of a cycle usually feels better than being pulled out of deep sleep. The calculator counts back (or forward) in whole cycles from your time and adds the minutes you take to fall asleep.

Bedtime = wake-up time − (cycles × 90 min) − time to fall asleep

The 90-minute figure is an average. Yours may be 80 or 100, so change the cycle length if you find a pattern. Consistent sleep and wake times matter more than the exact minute.

Good to know

Sleep runs in cycles of roughly 90 minutes that move from light to deep sleep and back through REM sleep. Waking at the end of a cycle usually feels easier than being woken in the middle of deep sleep, which causes grogginess.

Most adults need seven to nine hours, or four to six cycles. The calculator counts back or forward in 90-minute steps and adds the time you need to fall asleep. Cycle length varies between people and through the night, so treat the times as a starting point and adjust to how you feel. Persistent sleep problems should be discussed with a doctor, and this tool is not medical advice.