How to use the sleep calculator
- Under I want to, choose Wake up at or Go to bed at.
- Enter the Time, for example 07:00.
- Enter your Minutes to fall asleep (15 by default).
- Read the suggested times. The table lists options for 6, 5, 4 and 3 cycles, with the hours of sleep each one gives.
What it does and when to use it
Sleep is not one even block. Through the night you move through stages of non-REM sleep and REM sleep, and then the cycle starts again. The calculator counts in whole cycles so you can plan a bedtime or alarm that falls between them rather than in the middle of one.
It is useful when you have a fixed alarm and want to know when to go to bed, when you are going to bed late and want to choose an alarm, or when you are adjusting to an early start. If you are working on wider health goals, the BMI Calculator and TDEE Calculator cover weight and energy, and the Heart Rate Zone Calculator helps plan exercise.
How it works
- Wake up at: bedtime = wake-up time − (cycles × 90 minutes) − minutes to fall asleep
- Go to bed at: wake-up time = bedtime + minutes to fall asleep + (cycles × 90 minutes)
It does this for 6, 5, 4 and 3 cycles, which is 9, 7.5, 6 and 4.5 hours of sleep. The 90-minute length is the middle of the 80 to 100 minutes that the NHLBI gives for one cycle. Times wrap past midnight and are shown in both 24-hour and 12-hour form. Everything runs in your browser.
Worked examples
Waking at 07:00. With 15 minutes to fall asleep, five cycles means going to bed at 23:15: Bedtime for 5 cycles (7.5 h): 23:15 (11:15 pm). Six cycles moves bedtime to 21:45.
Going to bed at 23:00. Five cycles means Wake at for 5 cycles (7.5 h): 06:45 (6:45 am); six cycles means 08:15.
An early 06:00 start for someone who takes 30 minutes to fall asleep. Bedtime for 5 cycles (7.5 h): 22:00 (10:00 pm), or 20:30 for six cycles.
Limits and tips
- Cycles vary. 90 minutes is an average. If you often wake just before your alarm, try shifting your bedtime by 10 to 15 minutes.
- Short options are short. The 4.5-hour and 6-hour rows are there for nights when time is tight. They are below the CDC’s 7 hours for adults.
- Not for children. Children and teenagers need more sleep; the CDC lists their ranges by age.
- Not medical advice. If you snore loudly, stop breathing in your sleep, or feel very sleepy in the day despite enough time in bed, talk to a doctor.
Frequently asked questions
How long is a sleep cycle?
How much sleep do adults need?
Will waking at the end of a cycle make me less tired?
What should I enter for minutes to fall asleep?
Sources
- How Sleep Works — Sleep Phases and Stages (the cycle starts over every 80 to 100 minutes; usually four to six cycles a night) — National Heart, Lung, and Blood Institute, National Institutes of Health, accessed 2026-10-03
- About Sleep — recommended hours of sleep by age (adults 18–60 years, 7 or more hours) — Centers for Disease Control and Prevention, accessed 2026-10-03
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