Sleep Cycle Calculator
Waking mid-cycle is why 8 hours can feel worse than 7½. Time your night in 90-minute cycles and wake up between them.
How it works
Sleep runs in cycles of roughly 90 minutes, each moving through light sleep, deep sleep and REM. Waking at a cycle boundary — from light sleep — feels far easier than being pulled out of deep sleep by an alarm. The calculator adds the ~15 minutes an average adult takes to fall asleep, then counts whole cycles.
Frequently asked questions
How many cycles do I need?
Five to six cycles (7½–9 hours) suits most adults. Four (6 hours) works occasionally but builds sleep debt if it becomes routine.
Is everyone's cycle exactly 90 minutes?
No — real cycles run 80–110 minutes and lengthen through the night. Treat these times as good starting points and adjust by how you feel on waking; consistency matters more than precision.
What if I take longer than 15 minutes to fall asleep?
Shift the suggested bedtime earlier by the difference. Regularly needing 30+ minutes usually points to caffeine timing, screens or an inconsistent schedule.
Last updated: 2026-07-13