Free interactive tool
Sleep Cycle Calculator
Pick a wake-up time your brain agrees with — between cycles, not inside one.
Pick an alarm your brain agrees with
Set lights-out and how long you take to drift off; the wake windows land between ~90-minute cycles.
Sleep runs in cycles, not hours: waking between cycles feels lighter than waking inside deep sleep, which is why 7.5 hours can beat 8.
- Plan tonight: find the 5-cycle wake time for your real bedtime.
- Push lights-out 30 minutes later and watch every window shift.
Sleep runs in cycles of roughly 90 minutes, moving through light, deep, and REM stages. Waking between cycles usually feels lighter than an alarm landing mid-deep-sleep — which is why 7.5 hours can feel better than 8.
Set lights-out and how long you typically take to drift off; the tool lists wake times at 3, 4, 5, and 6 completed cycles so you can pick the alarm that fits your morning.
How long is one sleep cycle?
Around 90 minutes, though 80–110 minutes is all normal — treat the windows as targets, not laws.
How many cycles do I need?
Five cycles (7.5 h) suits most adults; teens generally need 8–10 hours, closer to six cycles.