Sleep Cycle Calculator
Find the perfect bedtime or wake time based on 90-minute sleep cycles. Wake up refreshed between cycles, not mid-dream.
About this tool
Enter your bedtime and this calculator works backwards from 90-minute cycles to show the best wake-up times — the ones that land on a natural cycle boundary, not in the middle of deep sleep.
Sleep debt is cumulative and waking refreshed is about timing as much as duration. Pick the wake time that fits your schedule and count back to the right bedtime.
FAQ
How do sleep cycles work?
Sleep runs in ~90-minute cycles (light, deep, REM). Waking at a cycle boundary, not mid-cycle, reduces grogginess.
How much sleep do I need?
Adults need 5-6 complete cycles — 7.5 or 9 hours — not just a fixed 8. Aim within 7-9 hours plus 10-20 minutes to fall asleep.
Is waking mid-cycle really worse?
Yes. Interrupted deep sleep leaves you with sleep inertia. Waking at a natural boundary feels noticeably lighter.