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Sleep Cycle Calculator

Plan approximate bedtimes or wake-up times from a target time.

Suggested bedtimes

These are approximate times based on 90-minute sleep cycles.

9 hours sleep

6 sleep cycles

9:45 PM

Previous evening

7.5 hours sleep

5 sleep cycles

11:15 PM

Previous evening

6 hours sleep

4 sleep cycles

12:45 AM

Same day

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How to use the Sleep Cycle Calculator

  1. 1. Choose whether you know the time you want to wake up or the time you plan to go to bed.
  2. 2. Enter that time and estimate how many minutes you normally take to fall asleep.
  3. 3. Compare the 4, 5 and 6-cycle options, then copy or share the times if useful.

Useful tips

  • • The calculator uses 90 minutes per cycle as a simple planning estimate. Real sleep cycles vary from person to person and across the night.
  • • NHLBI says sleep cycles commonly restart about every 80 to 100 minutes, so the displayed clock times should not be treated as exact biological boundaries.
  • • Healthy adults are generally advised to sleep at least 7 hours regularly, so the 4-cycle option is shorter than the usual adult sleep-duration recommendation.

Frequently asked questions

Why does the calculator use 90-minute cycles?

Ninety minutes is a convenient approximation, not a fixed rule. Sleep cycles can be shorter or longer, and cycle length changes during the night.

What does time to fall asleep change?

For a wake-time calculation it moves the suggested bedtime earlier. For a bedtime calculation it moves the estimated wake time later. The default is 15 minutes and can be changed from 0 to 60.

Why are 4, 5 and 6 cycles shown?

They correspond to about 6, 7.5 and 9 hours of estimated sleep time before adding sleep-onset time. They are planning options rather than personal sleep prescriptions.

Can this diagnose a sleep problem?

No. It only performs clock arithmetic. Persistent insomnia, excessive daytime sleepiness or other sleep concerns need appropriate professional assessment.

Is my sleep schedule uploaded?

No. The calculation runs in your browser and the entered times do not need to be sent to Wid9et.