Sleep Cycle Calculator
From a wake-up time or a bedtime, work out the times that let you wake up between 90-minute sleep cycles, not mid-cycle.
Daily LifeResult
Bedtime (5 cycles, 7h 30m sleep)
23:15
- Bedtime (6 cycles, 9h sleep)
- 21:45
- Bedtime (4 cycles, 6h sleep)
- 00:45
- Bedtime (3 cycles, 4h 30m sleep)
- 02:15
How is it calculated?
If you know your wake-up time, the tool counts back in 90-minute cycles and suggests a few bedtimes (with 15 minutes added to fall asleep). If you know your bedtime, it counts forward the same way and suggests wake-up times. Waking up mid-cycle tends to feel worse than waking up at the end of one, so every suggestion lands on a whole number of cycles.
Formula
Bedtime = Wake-up time − (cycles × 90 min) − 15 min Wake-up time = Bedtime + 15 min + (cycles × 90 min)
Example
What do you know?: I know my wake-up time · Wake-up time: 07:00 → Bedtime (5 cycles, 7h 30m sleep): 23:15
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Frequently asked questions
Is 90 minutes exact?
No, it's an average. A real sleep cycle can run anywhere from 70 to 120 minutes; this tool is a general guide, not a personal measurement.
Is this medical advice?
No. How much sleep you need depends on your age, health and how active your day is; see a professional if you have an actual sleep problem.
Why is 15 minutes added?
You don't fall asleep the instant you get into bed; it takes a few minutes on average. 15 minutes is a reasonable assumption for most people.
How many cycles are recommended?
For adults, 5 cycles (7.5 hours) is often considered a good middle ground; the tool shows a few options between 3 and 6 cycles, and it's up to you which fits.