Are sleep cycles exactly 90 minutes?

No—healthy adults average close to 90 minutes per cycle, but age, sleep debt, and disorders stretch or shrink phases.

Why add fall-asleep minutes?

Most people are not asleep the instant lights go out; we pad ~15 minutes before counting cycles.

Will this cure grogginess?

Sleep inertia depends on alarm placement, caffeine, chronic debt, and illness—use this as a planning hint only.

Does travel affect results?

Jet lag shifts circadian timing; reset schedules after time-zone jumps rather than trusting old cycle math.

Should I skip cycles for more sleep?

Total sleep still matters—sometimes an extra partial cycle beats waking strictly at cycle six.

Sleep Calculator — 90-Minute Cycle Bedtimes & Wake Times

Planning mode

Wake-up time

Minutes to fall asleep

Uses ~90-minute ultradian cycles plus your fall-asleep estimate—individual variation is normal.

😴

Set a reference time
to list cycle-aligned options

Suggested times

How to Use This Calculator

Choose whether you already know your alarm clock time or when you plan to get into bed.
Adjust fall-asleep minutes so cycle math starts near real sleep onset.
Compare multiple cycle counts and remember clinical sleep studies trump rough planners.

📐 Formula

Formula & Methodology

View formula, sources, and explanation+

Cycle length ≈ 90 minutes between ultradian peaks

Wake mode bedtime ≈ wake_time − fall_asleep_min − cycles × 90

Bed mode wake ≈ bedtime + fall_asleep_min + cycles × 90

Sleep staging varies night to night—use results as orientation, not medical timing.

❓ FAQ

Sleep FAQ

No—healthy adults average close to 90 minutes per cycle, but age, sleep debt, and disorders stretch or shrink phases.
Most people are not asleep the instant lights go out; we pad ~15 minutes before counting cycles.
Sleep inertia depends on alarm placement, caffeine, chronic debt, and illness—use this as a planning hint only.
Jet lag shifts circadian timing; reset schedules after time-zone jumps rather than trusting old cycle math.
Total sleep still matters—sometimes an extra partial cycle beats waking strictly at cycle six.

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