Sleep Cycle Calculator

A sleep cycle is one pass through the stages of sleep, from light sleep into deep sleep and then REM, lasting about 90 minutes. A full night is several cycles back to back. Most adults aim for five or six, which is roughly 7.5 to 9 hours.

Waking near the end of a cycle, when sleep is lightest, tends to feel easier than being pulled out of deep sleep mid-cycle. Timing your alarm to land between cycles can reduce that groggy, heavy feeling known as sleep inertia.

Cycles only start once you are actually asleep, and the average person takes around 14 minutes to drift off. The calculator adds that buffer so the suggested times line up with real cycle boundaries. You can change it if you fall asleep faster or slower.

No. The 90-minute cycle is an average and real cycles vary by person, age and night. Use the suggestions as a helpful target rather than a precise schedule, and adjust based on how rested you actually feel.

Most adults do well on five to six cycles, about 7.5 to 9 hours. The calculator highlights the most rested option first and lists shorter nights too, so you can pick what fits the time you have.

Yes. The calculation runs entirely in your browser. The times you enter are never sent to a server or stored anywhere, so nothing about your sleep leaves your device.