Sleep Cycle Calculator
Sleep cycles last about 90 minutes. Waking between cycles — instead of mid-deep-sleep — drastically reduces grogginess.
3 cycles · 4.5h
02:15 AM
Short
4 cycles · 6.0h
12:45 AM
Short
5 cycles · 7.5h
11:15 PM
Recommended
6 cycles · 9.0h
09:45 PM
Recommended
Sponsored
Frequently asked questions
How long is a sleep cycle?+
A complete sleep cycle averages 90 minutes, moving through light sleep, deep (slow-wave) sleep, and REM sleep. Healthy adults complete 5–6 cycles per night.
Why does waking mid-cycle feel awful?+
If your alarm fires during deep sleep, you experience sleep inertia — grogginess, slow reaction time, and impaired mood that can last 30+ minutes. Waking between cycles minimizes this.
Should I always wake at a cycle boundary?+
Generally yes, but consistency of sleep duration matters more than perfectly timed cycles. Use this calculator as a guide, not an obsession.
Does the 90-minute rule apply to everyone?+
It's an average — real cycles range from 80 to 110 minutes and shift across the night. REM cycles get longer toward morning.
How do sleep cycles change with age?+
Deep sleep peaks in childhood, declines steadily through adulthood, and may drop 70% by age 70. REM declines more gradually.
Can I increase deep sleep?+
Yes — exercise, cool bedrooms, alcohol abstinence, and avoiding late meals all reliably increase slow-wave sleep on polysomnography.
Why do I remember dreams some nights, not others?+
Dream recall is highest when you wake during or just after REM. Waking from deep sleep usually means no recall — even though you dreamed.
Sponsored