Pick a wake-up time and get the best bedtimes, or pick a bedtime and see when you will naturally surface. Based on 90-minute sleep cycles.
Everything runs locally in your browser. Your times never leave your device.
Times use the 24-hour clock — 22:30 means 10:30 PM.
For general information — not medical advice.
Sleep is not one flat block: it runs in repeating cycles of roughly 90 minutes. This planner counts in whole cycles either backwards from your alarm or forwards from your bedtime, and adds an average 15 minutes of time-to-fall-asleep on the bedtime side, so the plan targets waking at the end of a cycle rather than in the middle of one.
No — 90 minutes is a population average. In practice individual cycles typically run between about 80 and 110 minutes, and the first cycles of the night are shorter and deeper while the later ones carry more REM. Use 90 minutes as the starting grid, then fine-tune: if you keep waking groggy at the planned time, shift your bedtime by 15–20 minutes and see what a couple of weeks of real-world results say.
No — it is a scheduling aid, not a treatment. Going to bed at a consistent, cycle-aware time helps some people fall asleep faster and wake more easily, but insomnia has many causes (stress, light, caffeine, medical conditions) and persistent insomnia is treatable — cognitive behavioural therapy for insomnia (CBT-I) is the first-line recommendation in most guidelines. Talk to a healthcare provider if sleep problems last for weeks or affect your days.
Two nap lengths fit the cycle logic: about 20 minutes, which keeps you in light sleep and avoids waking from deep sleep, or a full ~90-minute cycle if you have the time. Anything in between — 40–70 minutes — is the most likely to leave you groggy, and long or late naps can eat into your night sleep.
It is handled correctly. Bedtimes and wake times are computed modulo 24 hours, so an alarm at 06:00 can give a bedtime of 23:15 the previous evening, and a 23:00 bedtime can give a 05:30 wake-up. Only the clock time is shown — the plan is assumed to start on the evening of your chosen day.
No. The whole tool is a few lines of vanilla JavaScript running in your browser. Your times never leave your device, and there is no account, no tracking and no network request attached to a calculation.
If you just finished with Sleep Cycle Calculator, the natural next steps are Breathing Timer, Ovulation Calculator, Pregnancy Due Date Calculator, or browse every tool in Health Tools.