The Science of Sleep Cycles
Sleep is not uniform — it occurs in repeating cycles of approximately 90 minutes, each containing distinct stages: light sleep (N1, N2), deep sleep (N3/slow-wave sleep), and REM (Rapid Eye Movement) sleep. Waking at the end of a complete cycle — rather than mid-cycle during deep sleep — is the key to feeling refreshed.
Sleep Stages Explained
| Stage | Type | Duration | Function |
|---|---|---|---|
| N1 | Light Sleep | 5–10 min | Transition to sleep, easy to wake |
| N2 | Light Sleep | 20 min | Heart rate slows, body temperature drops |
| N3 | Deep Sleep | 20–40 min | Physical restoration, immune function, growth hormone |
| REM | Dreaming | 10–60 min | Memory consolidation, emotional processing, creativity |
How Much Sleep Do You Need?
- Adults (18–64): 7–9 hours (5–6 complete cycles)
- Teenagers (14–17): 8–10 hours
- School children (6–13): 9–11 hours
- Older adults (65+): 7–8 hours
Tips for Better Sleep Quality
- Keep a consistent sleep schedule — same time every day including weekends
- Avoid screens 60 minutes before bed (blue light suppresses melatonin)
- Keep bedroom cool (18–20°C is optimal for sleep)
- Avoid caffeine after 2pm — its half-life is 5–7 hours
- Use our calculator to find a bedtime that aligns with natural 90-minute cycles