Sleep Calculator

Bedtimes or wake times in 90-minute cycles, with time to fall asleep

100% free. Runs entirely in your browser - your files and data never leave your device and nothing is uploaded to any server.

I want to

Clock

Go to bed at11:15 PM5 or 6 cycles is the usual adult target (~7.5 to 9 hours plus falling asleep)
4 cycles · 6.0 h sleep12:45 AM
3 cycles · 4.5 h sleep2:15 AM

Estimates only. Not medical advice and not a diagnosis. Talk to a clinician about your own numbers. Cycle length is a planning average, not EEG.

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About this tool

Sleep is often planned in 90-minute cycles. This tool subtracts (or adds) those cycles plus the minutes you say it takes to fall asleep. Five or six cycles is a common adult target, about 7.5 to 9 hours of sleep plus latency. Real sleep stages are not a metronome, and insomnia, shift work and sleep apnoea need clinical care. Estimates only. Not medical advice.

How to use this tool

  1. Choose wake time or bedtimeOne is the alarm; the other is when you get into bed.
  2. Set time to fall asleep15 minutes is a typical planning default. Chronic long latency is worth mentioning to a clinician.
  3. Pick 12-hour or 24-hour display12-hour mode shows AM and PM. The time picker itself stays 24-hour internally.
  4. Read 6, 5, 4 and 3 cycle optionsFive and six cycles are highlighted as the usual adult target.

Key features

  • Bedtimes for a fixed alarm, or wake times for a fixed bedtime.
  • 90-minute cycles plus a latency you control.
  • AM/PM or 24-hour labels.
  • Private in your browser.

Common uses

  • Picking a bedtime when the alarm is already set for 7:00.
  • Planning a nap-free night before an early flight.
  • Showing a teenager why 1:00 AM to 6:00 AM is only a few cycles.

Tips for better results

  • Keep the same wake time most days. The bedtime is the lever that usually moves.
  • Dim lights and skip caffeine in the evening; the calculator cannot fix those.
  • If you regularly need more than 30 minutes to fall asleep, talk to a clinician rather than adding more latency here.

Mistakes to avoid

  • Treating 90 minutes as EEG fact. It is a planning average.
  • Sleeping 3 cycles on weeknights and 6 on weekends, then blaming the calculator.
  • Using this page instead of care for loud snoring, gasping or falling asleep at the wheel.

Frequently asked questions

Most adults are told 7 to 9 hours. This page shows cycle options; it does not diagnose insomnia.

It is a planning average for a full NREM-REM cycle. Night-to-night EEG is messier than that.

The idea is to land the alarm near the end of a cycle so you feel less groggy. It does not always work. Consistency still beats a perfect clock.

Yes. It is free for normal use with no account required.

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