Back to Tools
Sleep Calculator
About the Sleep Calculator
Sleep runs in cycles of about 90 minutes. Waking at the end of a cycle usually feels easier than waking in the middle of deep sleep. This calculator suggests bedtimes or wake-up times that line up with those cycles.
How to use the Sleep Calculator
- Choose I want to wake up at and enter your wake-up time to find when to go to bed, or choose I am going to sleep at to find good wake-up times.
- Press Calculate Optimal Times.
- Pick one of the suggested times. Four to six cycles (6 to 9 hours) suit most adults.
Formula and method
Each cycle is 90 minutes and it takes about 15 minutes to fall asleep. Bedtime = wake time − (cycles × 90 min) − 15 min.
Worked example
To wake at 7:00 with 5 cycles (7.5 hours): 7:00 − 7 h 30 min − 15 min = 11:15 pm.
Tips
- Keep a regular sleep schedule, including weekends.
- Avoid caffeine in the afternoon and screens right before bed.
- Sleep needs vary. Most adults need seven to nine hours.
Frequently Asked Questions
Most adults do best on 7 to 9 hours. Teenagers need 8 to 10 and young children need more.
It is an average. Individual cycles range from about 80 to 110 minutes.