— Bedtime Calculator · 90-minute sleep cycle —
Find your optimal bedtime
Sleep happens in 90-minute cycles. Wake at the end of a cycle (REM/light sleep) and you wake refreshed; wake mid-cycle (deep N3) and you feel groggy. This calculator factors in the average 14 minutes to fall asleep.
Why 90-minute cycles?
Human sleep cycles through 4-6 phases of ~90 minutes each: N1 → N2 → N3 (deep) → REM (dream). Wake at the end of a cycle (when REM ends) and the transition feels natural; wake mid-N3 and you experience sleep inertia, a 30-60-minute fog of poor cognition.
Research from Harvard, Stanford, and the National Sleep Foundation confirms this. Most healthy adults do best with 5 cycles (7.5 hours) on weeknights or 6 cycles (9 hours) for full recovery.
Pro tip: The 14-minute "fall asleep" buffer is the average for healthy adults. If you're a Reflective (R) type (deep thinker), expect 20-30 minutes — adjust your bedtime accordingly. Take the 16-type test to know yours.
Tonight's checklist
- Go to bed 20-30 minutes before your target time
- Move your phone out of the bedroom
- Lights warm (amber) and dim 1 hour before bed
- Bedroom temperature: 18-20°C / 64-68°F
- Last caffeine: 6 hours before target bedtime
Want to go deeper?
Find your 16-type sleep personality to learn how YOUR body uses these cycles.