Sleep cycles, explained (and how to use them)

Sleep comes in ~90-minute cycles. Time your alarm to the end of one and the same hours feel dramatically better.

A full night of sleep isn't one long block — it's a stack of ~90-minute cycles, each moving from light sleep to deep sleep to REM and back. Most adults need 5 to 6 cycles a night (about 7.5–9 hours).

The rule that makes mornings easier

Time your bedtime so your alarm lands at the end of a cycle, not the middle. Working backward from your wake time, count back in 90-minute blocks and add ~15 minutes to fall asleep.

If you wake at	Go to bed at (6 or 5 cycles)
5:30 AM	9:00 / 10:30 PM
6:00 AM	9:30 / 11:00 PM
6:30 AM	10:00 / 11:30 PM
7:00 AM	10:30 PM / 12:00 AM
7:30 AM	11:00 PM / 12:30 AM
8:00 AM	11:30 PM / 1:00 AM

Times assume ~15 minutes to fall asleep. Your real cycle length varies night to night (80–110 min), so treat these as a strong starting point, not a stopwatch.

What throws cycles off

Caffeine — it has a ~5-6 hour half-life, so a 3pm coffee is still half-active at bedtime.
Late screens / bright light — delays melatonin and pushes your first cycle later.
Alcohol — helps you fall asleep but fragments the back half of the night, cutting REM.

Find my cycle-aligned bedtime