Health Calculators
Sleep cycle calculator.
Pick the time you need to wake up, or the time you are going to bed. Get times that line up with about 90-minute sleep cycles, marked against the sleep hours recommended for your age. Runs in your browser; nothing is sent or stored.
Your sleep
Suggested times
Fill the form and press Show times.
How the times are worked out
- Cycle length: one sleep cycle is taken as 90 minutes, the average reported in sleep-medicine textbooks. Real cycles range roughly 70 to 110 minutes and change across the night, so treat the times as planning targets, not exact.
- Falling asleep: your time to fall asleep is added to each option (default 15 minutes).
- Waking time given: bedtime = wake-up time − (cycles × 90 min) − time to fall asleep. Bedtime given: wake-up = bedtime + time to fall asleep + cycles × 90 min.
- Age check: each option shows its total sleep in hours and is marked when it falls inside the recommended range for your age.
Worked example. Wake at 7:00 AM, 15 minutes to fall asleep: 5 cycles (7.5 h) means bed at 11:15 PM; 6 cycles (9 h) means 9:45 PM.
Recommended sleep by age
The ranges include naps for the youngest ages (24-hour totals for under-3s). Sources (opened 2026-10-04): Paruthi et al., J Clin Sleep Med 2016;12(6):785-786 (AASM, ages 4 months to 18 years); Watson et al., Sleep 2015;38(6):843-844 (AASM and Sleep Research Society: adults 7 or more hours); Hirshkowitz et al., Sleep Health 2015;1(1):40-43 (National Sleep Foundation: 18 to 64 years 7 to 9 hours, 65+ 7 to 8 hours).
FAQ
How long is a sleep cycle?
About 90 minutes on average in adults, moving through lighter sleep, deeper sleep and REM sleep. It varies between people and across the night, so this calculator uses 90 minutes as a planning figure.
How many sleep cycles do I need?
It depends on age. Most adults aged 18 to 64 are advised 7 to 9 hours, which is 5 or 6 cycles of 90 minutes. The calculator marks the options that fall in the recommended range for the age you enter.
What time should I go to bed if I wake at 6 AM?
With 15 minutes to fall asleep, 5 cycles means bed at 10:15 PM and 6 cycles means 8:45 PM. Enter 06:00 above to see your own options.
Will I wake up refreshed if I wake at the end of a cycle?
It may help some people, but there is no guarantee. How you feel also depends on sleep debt, sleep quality and the time of day. Total sleep matters more than hitting an exact cycle boundary.
Does this work for naps?
Not specifically. It is built around full night-time sleep. For a short nap, a common planning length is under 30 minutes, but this tool does not model naps.
Disclaimer
Educational estimate, not medical advice. Persistent trouble sleeping, loud snoring, or being very sleepy in the day can have medical causes; talk to a doctor or pharmacist about it. This tool does not diagnose a sleep disorder.