Sleep cycle bedtime calculator

Fix your alarm, then count backward in 90-minute cycles from that wake time. Subtract your usual sleep latency so “lights out” lands where sleep onset should begin — a practical way to avoid waking from slow-wave sleep mid-cycle.

Target wake timeSleep latency (min)Time from lights out to sleep onset.

Wake locked at 07:00. Each row is a full-cycle night length ending in that wake time.

4 cycles · 6.0 h sleep
Lights out 00:45Onset ~01:00
5 cycles · 7.5 h sleep
Lights out 23:15Onset ~23:30
6 cycles · 9.0 h sleep
Lights out 21:45Onset ~22:00
7 cycles · 10.5 h sleep
Lights out 20:15Onset ~20:30
8 cycles · 12.0 h sleep
Lights out 18:45Onset ~19:00

Educational estimates only. Sleep and caffeine metabolism vary widely. This is not medical advice; talk to a clinician if you have insomnia, apnea, or other conditions.