Sleep Cycle Calculator
Sleep happens in ~90 minute cycles. Waking at the end of a cycle feels far more restful than mid-cycle. Pick whether you want to wake up at a specific time, or you're going to bed now.
Try going to bed at one of these times
Why 90 minutes
A complete sleep cycle averages 90 minutes for adults (range: 70–120). You move through light → deep → REM and back. Waking in deep sleep produces the groggy "sleep inertia" we all hate. Waking at the boundary between cycles, when sleep is lightest, is the goal.
How many cycles do I need?
Most adults function well on 5–6 cycles (7.5–9 hours). 4 cycles is the survival minimum for a single night; less for multiple nights breaks down concentration and mood. 3 cycles is "I'll catch up tomorrow" mode.
The 14-minute buffer
We add 14 minutes for falling asleep — the population median. Adjust mentally if you're a quick-asleep type (subtract) or a slow-sleeper (add).