About the sleep calculator
Sleep runs in cycles of roughly 90 minutes, moving from light to deep to REM sleep. Waking at the end of a cycle usually feels easier than being pulled out of deep sleep. This calculator counts back (or forward) in 90-minute steps and adds the time it takes you to fall asleep.
Formula
Bedtime = wake-up time − (number of cycles × 90 min) − time to fall asleep.
Frequently asked questions
How many sleep cycles do I need?
Most adults do well with 5 or 6 cycles, which is 7.5 to 9 hours.
What time should I go to bed to wake up at 6 AM?
Set the wake-up time to 6:00 AM. For 5 cycles, the calculator suggests about 10:15 PM with a 15-minute fall-asleep time.