Why sleep cycles matter more than hours
Your night isn't one long block of sleep — it's a series of 90-minute cycles, each moving from light sleep into deep sleep and then REM. You cycle through five or six of these before morning.
The trick to waking up refreshed is waking at the end of a cycle, when you're already in light sleep — not being dragged out of deep sleep by an alarm. That's why 7.5 hours (5 cycles) can feel better than 8 hours (which lands you mid-cycle).
Bedtime = wake time − (n × 90 min) − time to fall asleep
Good targets: n = 5 or 6 cycles (7.5–9 hours)
Good targets: n = 5 or 6 cycles (7.5–9 hours)
How to use the results
We add your average time to fall asleep (about 14 minutes for most people) and then count back or forward in 90-minute blocks. Pick a time that gives you 5 or 6 full cycles and try to hit it consistently.
Cycles average 90 minutes but vary person to person (80–110 min). Treat these times as smart targets, then notice which one leaves you feeling best and lean into it.
Better sleep, beyond timing
- Same time every day — even weekends. Regularity is the foundation everything else builds on.
- No screens for the last 30–60 minutes — bright light delays the melatonin that makes you drowsy.
- Cool, dark, quiet — around 18°C is ideal for most sleepers.
- Cut caffeine after early afternoon — it has a ~6-hour half-life and lingers longer than you'd think.