Sleep Cycle Calculator
Enter your wake-up time to find the best bedtimes that align with complete 90-minute sleep cycles.
How Sleep Cycles Work
Sleep is not a uniform state — it progresses through repeating stages:
- N1 (Light sleep) — transition to sleep, easily woken
- N2 (Light sleep) — body temperature drops, heart rate slows
- N3 (Deep sleep) — most restorative, immune repair, memory consolidation
- REM — dreaming, emotional processing, learning
Each cycle takes approximately 90 minutes. In the first half of the night, deep sleep dominates. In the second half, REM sleep increases.
Sleep Recommendations by Age
| Age Group | Recommended Sleep |
|---|---|
| Teenagers (14–17) | 8–10 hours |
| Young adults (18–25) | 7–9 hours |
| Adults (26–64) | 7–9 hours |
| Older adults (65+) | 7–8 hours |