A full sleep cycle (light → deep → REM) averages about 90 minutes. Waking at the end of a cycle, rather than mid-deep-sleep, usually feels much better.

Sleep Calculator

Find the best bedtime or wake-up time based on 90-minute sleep cycles.

Wake-Up Time

Sleep runs in ~90-minute cycles; waking between cycles feels easier. Includes ~15 minutes to fall asleep.

9:45 PM

6 cycles · 9 h · recommended

11:15 PM

5 cycles · 7.5 h · recommended

12:45 AM

4 cycles · 6 h

2:15 AM

3 cycles · 4.5 h

DISCLAIMER: Cycle lengths vary from person to person; treat these as starting points. Adults generally need 7–9 hours. Not medical advice.

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What Is the Sleep Calculator?

The Sleep Calculator works backwards (or forwards) in 90-minute sleep cycles — plus about 15 minutes to fall asleep — to suggest bedtimes or wake-up times that land between cycles, when waking feels easiest.

How It Works

Pick whether you know your wake-up time or your bedtime, set the time, and see four suggestions ranked by cycles of sleep.

When to Use It

Use it before an early alarm, a flight or an exam to wake up feeling refreshed instead of groggy.

Frequently Asked Questions

Why 90 minutes?: A full sleep cycle (light → deep → REM) averages about 90 minutes. Waking at the end of a cycle, rather than mid-deep-sleep, usually feels much better.

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