Sleep Cycle Calculator

Sleep cycle basics

• ~90 minutes per cycle — light sleep → deep sleep → REM → back to light
• 5-6 cycles per night for adults (7.5-9 hours)
• Waking at the end of a cycle feels natural — light sleep, easy to rise
• Waking mid-cycle (especially in deep sleep) causes "sleep inertia" — groggy for 30+ minutes

The 14-minute rule

Most people take 10-20 minutes to fall asleep — the calculator defaults to 14. If you typically fall asleep faster (or slower), adjust the slider. Insomniacs can take 45-60+ minutes.

4.5h naps are a thing

If you have to nap and can't get a full 90-min cycle, three 90-min cycles (4.5h) feels surprisingly good — better than 6h that lands mid-cycle. Same logic.

Not medical advice

This is a guideline based on average cycle length. Real cycles vary by age, alcohol, caffeine, stress, and many other factors. For sleep disorders see a doctor.

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