Sleep Calculator
Want to wake up at the end of a sleep cycle instead of in the middle of one? Find the bedtime or wake-up time that fits full cycles, with at least 7 hours of sleep.
Your details
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Pick a time to see when to go to bed or wake up.
| Bedtime | Sleep | Cycles |
|---|
Cycles average about 90 minutes but vary from person to person and through the night, so treat these times as a guide. Adults need 7 hours or more.
How to use it
- Choose whether you know your wake-up time or your bedtime, and enter it.
- Optionally change how long it usually takes you to fall asleep (15 minutes by default).
- Read the suggested time for 5 cycles (7.5 hours), and the options for 4 and 6 cycles.
How it's calculated
The cycles. Sleep moves through stages of non-REM and REM sleep in repeating cycles. The first cycle lasts about 70 to 100 minutes and later ones about 90 to 120 minutes, averaging roughly 90 (Carskadon & Dement). The calculator uses 90 minutes.
The formula. To wake at a set time:
bedtime = wake-up time − (cycles × 90 min) − time to fall asleep
Example: to wake at 7:00 after 5 cycles, with 15 minutes to fall asleep: 7:00 − 7 h 30 min − 15 min = 23:15. Going to bed at a set time works the same way in reverse.
How much. The AASM and Sleep Research Society recommend 7 or more hours a night for adults (Watson et al. 2015). Five cycles (7.5 hours) is the first option that meets that, so it’s the suggestion. Four cycles (6 hours) is shown for reference but marked as under 7 hours.
Limits. Cycle length varies between people and across the night, and the time it takes to fall asleep changes from night to night, so these times are a guide, not a precise alarm. If you struggle with sleep regularly, talk to your doctor.
Sources
- Watson, N. F., Badr, M. S., Belenky, G., et al. (2015). Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Journal of Clinical Sleep Medicine, 11(6), 591–592.
- Carskadon, M. A., & Dement, W. C. Normal human sleep: an overview. In Kryger, Roth & Dement (Eds.), Principles and Practice of Sleep Medicine.
- Institute of Medicine (2006). Sleep Disorders and Sleep Deprivation, chapter 2: Sleep physiology.
Questions
How much sleep do I need?
Adults should sleep 7 or more hours a night, according to the American Academy of Sleep Medicine and the Sleep Research Society. Some people, especially young adults, need more than 9.
Why 90-minute cycles?
Through the night you move through light sleep, deep sleep and REM sleep in cycles of about 90 minutes. Waking at the end of a cycle may feel easier than waking from deep sleep.
Is 6 hours enough if it's 4 full cycles?
No. Full cycles don't make up for too little sleep. Regularly sleeping under 7 hours is linked to worse health and performance.
Does sleep affect my training?
Yes. Short sleep is linked to impaired performance and slower recovery, so getting enough is one of the simplest ways to train better.
Updated November 9, 2026.