Sleep Cycle Calculator

How It Works

Sleep runs in cycles of about 90 minutes, moving from light sleep through deep sleep and dreaming (REM) and back. Waking in the middle of a cycle — especially deep sleep — is what leaves you groggy, even after eight hours in bed. Waking between cycles, at the end of a light-sleep phase, usually feels far easier. This calculator counts in whole 90-minute cycles and allows about 15 minutes to fall asleep.

Give it your bedtime and it shows wake-up times completing 4, 5 or 6 cycles — 6, 7.5 or 9 hours of sleep. Give it your alarm time and it works backwards to the matching bedtimes. Five or six cycles suit most adults; four is a short night.

Worked Example

Going to bed at 10:30 PM and falling asleep around 10:45 PM, four cycles end at 4:45 AM, five at 6:15 AM and six at 7:45 AM — so 7:45 AM is the best alarm time for a full night. Working backwards from a 7:00 AM alarm, the bedtimes are 9:45 PM for six cycles, 11:15 PM for five and 12:45 AM for four.

How to Use This Calculator

Choose whether to start from your bedtime or your alarm, enter the time, and you get the matching times for 4, 5 and 6 cycles. Pick the option that fits your schedule — and if two times look possible, the one with more cycles is usually the better choice.

Tips and Practical Advice

Keep the same sleep and wake times most days — a regular rhythm matters more than one night’s timing. If you usually take longer than 15 minutes to fall asleep, shift bedtime earlier by the difference. And 90 minutes is an average: if you keep waking groggy at a “correct” time, your cycles may run shorter or longer.

Source: sleep cycles of about 90 minutes, with about 15 minutes allowed to fall asleep. Reviewed Nov 13, 2026.

Frequently Asked Questions