Sleep Calculator
Find the best bedtime or wake-up time with 90-minute sleep cycles and a realistic 15-minute fall-asleep buffer.
Find the best bedtime or wake-up time without counting sleep cycles by hand
Mode
Wake-up time
These results assume it takes about 15 minutes to fall asleep and each sleep cycle lasts about 90 minutes.
Recommended bedtimes
Based on waking up at 6:30.
21:15
6 sleep cycles
About 9h 15m in bed
22:45
5 sleep cycles
About 7h 45m in bed
0:15
4 sleep cycles
About 6h 15m in bed
1:45
3 sleep cycles
About 4h 45m in bed
3:15
2 sleep cycles
About 3h 15m in bed
4:45
1 sleep cycles
About 1h 45m in bed
How to use the results
Most adults feel best after 5 or 6 full sleep cycles. Start with the first two recommended options, then use the shorter windows only when your schedule is tighter.
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Frequently Asked Questions
How does the sleep calculator work?
It adds a 15-minute buffer for falling asleep and then counts backward or forward in 90-minute sleep cycles.
Why are there six suggested times?
Six options lets you compare 1 to 6 full sleep cycles, with the longest and most practical options shown first.
Why are the first two times recommended?
For most adults, 5 or 6 complete sleep cycles usually feels better than shorter sleep windows.
Does this guarantee I will wake up refreshed?
No. This is a planning estimate based on average sleep-cycle timing. Stress, caffeine, illness, naps, and schedule changes can all affect sleep quality.