Sleep schedule
Bedtime Calculator
Sleep runs in repeating cycles of light sleep, deep sleep and REM sleep that last roughly 90 minutes on average. Waking at the end of a cycle, rather than in deep sleep, may help you feel less groggy. Enter your wake time and this calculator counts back whole cycles, plus the minutes you usually need to fall asleep, to suggest bedtimes. Six cycles (9 hours) or five cycles (7.5 hours) fit the 7 or more hours that adults need; four cycles (6 hours) is short for most adults.
How it works
Bedtime = wake time minus (number of cycles x cycle length) minus the minutes it takes you to fall asleep. Times wrap around midnight, so a result before 12:00 AM shows as the evening before.
Example
Wake time 7:00 AM, 15 minutes to fall asleep, 90 minute cycles. Six cycles is 540 minutes, so 7:00 AM minus 9 h minus 15 min = 9:45 PM. Five cycles gives 11:15 PM and four cycles gives 12:45 AM.
Assumptions and limits
- A sleep cycle averages about 90 minutes but commonly ranges from about 70 to 120 minutes, and cycles change across the night (more deep sleep early, more REM late).
- Most adults fall asleep within about 10 to 20 minutes; enter your own typical time.
- The CDC recommends 7 or more hours for adults aged 18 to 60, so 4 cycles (6 hours) is below the recommendation.
- This is a planning aid. A consistent schedule and enough total sleep matter more than landing on an exact cycle boundary.
Frequently asked questions
Is a sleep cycle always 90 minutes?
No. About 90 minutes is a common average, but individual cycles usually run about 70 to 120 minutes and vary through the night. Adjust the cycle length field if you know your own pattern, and treat the results as approximate.
Which bedtime should I choose?
For most adults, 5 cycles (7.5 hours) or 6 cycles (9 hours) of sleep fits the recommendation of at least 7 hours. Pick the one you can keep every night, including weekends, because a regular schedule helps your body clock.
What if I cannot fall asleep at the suggested time?
Going to bed when you are not sleepy can make insomnia worse. If you lie awake for a long time, getting up and doing something quiet until you feel sleepy is a core part of insomnia treatment (stimulus control). Ongoing trouble falling asleep is worth discussing with a clinician.
Why add time to fall asleep?
The time between lights out and actually falling asleep is called sleep latency. Adding it means the cycles start when you are asleep, not when you get into bed.
Sources
Tools and screening scores are general information. They cannot diagnose or rule out a sleep disorder. Read our medical disclaimer.