Sleep Calculator
Plan bedtimes and wake-ups around sleep cycles — locally, in your browser.
No signup · No uploads · Calculations stay on your device
Enter the time your alarm goes off.
Suggested bedtimes for a 7:00 AM wake-up
- 9:45 PMtonight
- 11:15 PMtonightClosest to 8 h
- 12:45 AMtoday
- 2:15 AMtoday
Advanced sleep planner
Total sleep time matters more than matching an estimated cycle.
A planning estimate, not a prediction of REM phases or medical advice. Age group is not saved. NIH
Results are planning estimates built from average sleep-cycle lengths and a configurable time-to-fall-asleep. They are not medical advice, not a sleep diagnosis, and not a guarantee that you will fall asleep or wake up on cue.
Sleep cycle calculator: bedtime and wake-up estimates
Sleep typically arrives in repeating cycles of roughly 90 minutes (light sleep, deep sleep, REM), and most adults take about 15 minutes to fall asleep after lights out. This tool works those two averages into simple planning arithmetic: pick the time you want to wake up and it suggests bedtimes for 3–6 full cycles, or pick a bedtime (or "sleep now") and it suggests wake-up times. You can adjust both assumptions — time to fall asleep and cycle length — in the form, and the estimates update instantly.
The results are planning estimates, not medical advice. They do not measure your sleep architecture, cannot diagnose a sleep problem, and do not guarantee you will fall asleep or wake at the suggested minute. If you regularly struggle to sleep well, talk to a qualified health professional. Every calculation happens on your device: there is no account and no server request for the calculation. The browser may remember your selected mode, times, onset estimate and cycle length in local storage so the calculator reopens with your preferences; those settings stay on your device and can be cleared with this site's browser data. Read the Privacy Policy.
About 90-minute sleep cycle estimates and REM sleep
People often search for a 90 minute sleep cycle calculator or a REM sleep calculator. This tool can use 90 minutes as a planning assumption, but real sleep cycles vary between people and across the night. REM is one part of normal sleep architecture, and a browser calculator cannot measure when you actually enter or leave REM sleep.
Use the suggested times as a schedule-planning aid rather than a diagnosis or a promise of better sleep. If you need a quick explanation of the controls and assumptions, read the Sleep Calculator guide.
Sleep calculator FAQ
Is every sleep cycle exactly 90 minutes?
No. Ninety minutes is a common planning estimate, not a fixed biological rule. Change the cycle length in the calculator if you want to compare different assumptions.
Can this calculate my REM sleep?
No. It can estimate clock times from a chosen cycle length, but it cannot measure sleep stages or determine when you are actually in REM sleep.
Can I use this as a wake up time calculator?
Yes. Enter a bedtime, choose your estimated time to fall asleep and cycle length, and the calculator shows several possible wake-up times.
Can I use this as a nap calculator?
You can use the “sleep now” flow to compare clock times based on your chosen cycle length, but naps do not always follow full sleep cycles. Treat the result as a planning estimate, not a medical recommendation.