Health
Sleep Calculator
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Find the best wake-up times based on your bedtime and 90-minute sleep cycles. Free sleep calculator — no account required, runs in your browser.
Comment utiliser cet outil
- Enter the time you plan to go to bed, or the time you need to wake up.
- The tool counts back or forward in 90-minute sleep cycles, allowing about 15 minutes to fall asleep.
- Read the suggested times that land at the end of a full cycle.
Optimal wake-up times
4.5 hours (3 cycles)
02:45
6 hours (4 cycles)
04:15
7.5 hours (5 cycles)
Ideal05:45
9 hours (6 cycles)
Ideal07:15
Includes 15-minute sleep onset buffer. Waking between cycles helps you feel more rested.
Questions fréquentes
- How does it pick the times?
- Sleep moves through cycles of about 90 minutes, so waking at the end of a cycle tends to feel less groggy than waking mid-cycle. The tool counts whole 90-minute cycles from your bedtime (or back from your wake time) and adds about 15 minutes to fall asleep.
- Why several suggested times instead of one?
- Different people need a different number of cycles, so it lists options — typically five or six cycles, or about 7.5 to 9 hours.
- Is the 90-minute figure exact?
- It is an average; real cycles range roughly 80–120 minutes and shift through the night, so the times are a helpful approximation rather than a precise schedule.
- Are my bedtime entries stored?
- No. The cycle arithmetic happens in your browser and the times you type are never transmitted or saved.