Tools
Health & Fitness
Sleep Time Calculator
Best bedtimes and wake-up times based on 90-minute sleep cycles.
Wake up at…
Wake-up time
Enter a wake-up time
Sleep at…
Bedtime
Enter a bedtime
Sleep Cycles
One cycle = 90 minutes
Sleep happens in repeating 90-minute cycles. Waking mid-cycle leaves you groggy; waking at the end of a cycle feels natural.
| Stage | Duration |
|---|---|
| N1 Light | 1–7 min |
| N2 Light | 10–25 min |
| N3 Deep | 20–40 min |
| REM | 10–60 min |
Adults need 7–9 hours
That's 5–6 full sleep cycles per night. Less than 4 cycles impairs memory and focus.