Sleep Cycle
Sleep Cycle — runs in your browser. Inputs are not stored.
Sleep-cycle bedtime
Enter values, then press Calculate.
Assumes 90-minute sleep cycles. Individual results vary; this is not medical advice.
How to use
- Enter a wake time. The default is 07:00.
- Enter minutes to fall asleep. The default 15 minutes is buffer from lights out until you fall asleep.
- Press Suggest to list bedtimes from 6 cycles down to 3. Six cycles are 9 hours; three are 4.5 hours.
- Pick one time to set an alarm. If you cannot sleep, compare one cycle later.
- Naps and shift work may not fit this assumption. This is not medical advice.
Key concepts
The sleep cycle calculator is for “what time should I sleep,” a 90-minute sleep cycle, and working backward from wake time. It assumes a classic NREM/REM cycle of 90 minutes and subtracts cycles × 90 minutes plus fall-asleep minutes from wake time. It lists 6 cycles (9 hours) down to 3 cycles (4.5 hours).
Real cycle length often varies from 70–120 minutes. Sleep disorders, medication, and shift work are not solved by this table alone. This is not medical advice. Calculation is local.
Example
Wake 07:00, 15 minutes to fall asleep → 6 cycles (9 hours) bedtime previous day 21:45, 5 cycles 23:15, 4 cycles 00:45, 3 cycles 02:15. Raising fall-asleep to 30 minutes pulls every time 15 minutes earlier. You do not have to sleep at these times. Wake 06:30 with 20 minutes to fall asleep → 6-cycle bedtime around previous day 21:10. Setting fall-asleep to 0 pushes every time 20 minutes later.
Notes
These results are not a medical diagnosis or treatment advice. Discuss health, pregnancy, and nutrition decisions with a clinician.
Related: Body fat calculator · Calorie calculator (BMR·TDEE) · Water intake calculator
Frequently asked questions
Why is a sleep cycle 90 minutes?
It is a classic textbook assumption for cycle length. Individual differences are large. It may differ from your sleep-app cycles.
How are minutes-to-fall-asleep used for bedtime?
They are subtracted from cycle time in advance. Enter the real time from lights out until you fall asleep.
Does it calculate nap sleep cycles too?
It is mainly for overnight bedtimes. You can enter a time with the same formula, but the intended use is nighttime.
Are sleep times sent to a server?
No. Calculation runs only in the browser. Wake time is not stored.
Do I have to follow the suggested bedtime?
No. It is a reference schedule. You do not have to set the alarm to that exact time.
Are in-between totals like 7 hours shown?
Only 3–6 cycles (4.5–9 hours) are listed. 7 hours is not on this list.
Last reviewed: 2026-09-04