Sleep Calculator
Find a bedtime or wake-up time that fits full sleep cycles. Choose the time you want to wake up or go to bed, and see the best times for 5 or 6 sleep cycles.
Go to bed at
9:45 PM or 11:15 PM
5 or 6 cycles (7 h 30 min to 9 h of sleep)
Check the highlighted fields to see your result.
All options
| Cycles | Time | Sleep |
|---|---|---|
| 6Recommended | 9:45 PM | 9 h 00 min |
| 5Recommended | 11:15 PM | 7 h 30 min |
| 4 | 12:45 AM | 6 h 00 min |
| 3 | 2:15 AM | 4 h 30 min |
Results are estimates for information only and do not constitute financial, medical, or legal advice.
How sleep cycles work
During the night you go through several sleep cycles, each one about 90 minutes long on average. Waking up at the end of a cycle, when your sleep is lighter, usually feels easier than waking up in the middle of deep sleep.
The calculator counts back (or forward) whole cycles from the time you enter and adds the minutes it takes you to fall asleep. The results are general information, not medical advice.
The formulas
Bedtime = wake-up time − cycles × 90 min − time to fall asleep
Wake-up time = bedtime + time to fall asleep + cycles × 90 min
Worked example
You want to wake up at 7:00 AM and it takes you 15 minutes to fall asleep.
- 6 cycles: 6 × 90 = 540 min = 9 h. 7:00 AM − 9 h − 15 min = 9:45 PM.
- 5 cycles: 5 × 90 = 450 min = 7 h 30 min. 7:00 AM − 7 h 30 min − 15 min = 11:15 PM.
Frequently asked questions
Is a sleep cycle always 90 minutes?
No. Cycles usually last somewhere between about 80 and 120 minutes and vary from person to person and through the night. 90 minutes is a common average, so treat the times as a starting point and adjust them to how you feel.
How much sleep do I need?
Health organizations generally recommend that adults get at least 7 hours of sleep a night. Five or six 90-minute cycles (7 h 30 min to 9 h) fit that recommendation.
What if I don't fall asleep in 15 minutes?
Change "Minutes to fall asleep" to the time it usually takes you. If you often have trouble sleeping, talk to a doctor.