Sleep Calculator
Sleep Calculator
Sleep moves through ~90-minute cycles. Waking mid-cycle leaves you groggy — waking between cycles doesn't. Pick a time below to find your window.
Through the night you move through light sleep, deep sleep, and REM in a repeating loop that lasts roughly 90 minutes.
If your alarm interrupts deep sleep, you'll feel foggy even after a full night. Waking between cycles avoids that.
Give it a wake-up time or a bedtime, and it lines up options in clean 90-minute increments, plus a buffer to actually fall asleep.
The typical length of one full sleep cycle, from light sleep through REM and back again.
Complete cycles most adults need in a night to wake up feeling genuinely rested.
Average time it takes a person to fall asleep after getting into bed.
The general nightly range most health guidelines recommend for adults.
Ranges reflect general sleep-health guidance and vary by individual. Cycle counts assume ~90-minute cycles and don't apply to very young children, whose sleep architecture differs.
Going to bed and waking up at the same time daily, even on weekends, helps your body settle into a stable cycle rhythm.
Bright light, especially from screens, delays the release of melatonin and can push your natural bedtime later.
Caffeine can stay in your system for 6+ hours, so an afternoon coffee can still be affecting your sleep onset at night.
A cooler room (around 65°F / 18°C) and minimal light both support deeper, less interrupted sleep cycles.
Eight hours is a good average, but it doesn't always land on a clean cycle boundary. Six cycles of 90 minutes is 9 hours, five cycles is 7.5 — both tend to feel better than an arbitrary 8-hour cutoff that ends mid-cycle.
No — it's a population average. Individual cycles can run anywhere from about 70 to 120 minutes, and can shift with age, stress, or sleep debt. Treat the results as a strong starting estimate, not a guarantee.
Four cycles (about 6 hours) is on the low end but still respects cycle boundaries, so it's usually better than an odd number of hours. It's not a substitute for consistently getting enough sleep, though.
Short naps (20-30 min) work differently since they aim to avoid deep sleep entirely, so you skip grogginess on waking. A full 90-minute nap can also work well since it completes one cycle.