Sleep Cycle Calculator

About this calculator

This tool schedules bedtimes or wake-up times around the body's natural 90-minute sleep cycle, the recurring pattern of light sleep, deep sleep and REM that repeats through the night. Waking up mid-cycle, especially during deep sleep, tends to produce grogginess ("sleep inertia"), while waking near the boundary between cycles usually feels much easier, even with the same total number of hours slept.

It is used by anyone trying to time an alarm more intelligently, students and shift workers planning naps or early mornings, and parents working backward from a wake-up time to find the best bedtime for a child. The calculator also adds roughly 15 minutes to account for the time it typically takes to actually fall asleep, so the suggested times reflect when to actually get into bed rather than just when to close your eyes.