How Sleep Cycles Work and How to Time Your Bedtime

During the night, sleep moves through repeating cycles of lighter sleep, deep sleep and REM sleep. A full cycle averages about 90 minutes, although it varies from person to person and across the night.

Counting back from your alarm

A simple approach is to count whole cycles backward from your wake-up time and add about 15 minutes to fall asleep. For a 7:00 AM alarm, five cycles points to a bedtime around 11:15 PM, six cycles to about 9:45 PM, and four cycles to about 12:45 AM.

Why timing is only part of it

• Most adults do best with at least 7 hours of sleep.
• A consistent schedule matters more than hitting exact cycle marks.
• Light, caffeine, alcohol and screens late in the day can disrupt sleep.

The 90-minute figure is an average, so treat the results as a starting point. If you have persistent sleep problems, talk to a healthcare professional. This article is general information, not medical advice.