😴 Sleep Calculator
Find the ideal times to sleep or wake up to complete full sleep cycles and wake up feeling refreshed.
Sleep Cycle Science
Each sleep cycle lasts approximately 90 minutes and passes through four stages:
| Stage | Type | Duration | Purpose |
|---|---|---|---|
| Stage 1 | Light Sleep (N1) | 5–10 min | Transition to sleep |
| Stage 2 | Light Sleep (N2) | 20 min | Heart rate slows, body cools |
| Stage 3 | Deep Sleep (N3) | 20–40 min | Physical restoration, immunity |
| Stage 4 | REM Sleep | 10–20 min | Memory consolidation, dreaming |
Recommended Sleep by Age
| Age Group | Recommended Hours | Cycles |
|---|---|---|
| Newborn (0–3 mo) | 14–17 hours | 9–11 |
| School Age (6–12) | 9–11 hours | 6–7 |
| Teenager (13–18) | 8–10 hours | 5–6 |
| Adult (18–64) | 7–9 hours | 4–6 |
| Older Adult (65+) | 7–8 hours | 4–5 |
Frequently Asked Questions
How many hours of sleep do I need?
Adults need 7–9 hours (4–6 cycles). Teens need 8–10 hours. Children 9–11 hours. Quality matters as much as quantity — complete cycles are key.
What is a sleep cycle?
A 90-minute cycle includes light sleep, deep sleep, and REM dreaming stages. Waking between cycles (not mid-cycle) leaves you feeling alert and refreshed.
Why am I tired after 8 hours of sleep?
You likely woke mid-cycle. Try 7.5 hrs (5 cycles) or 9 hrs (6 cycles) instead. Also check for sleep apnea, caffeine after 2pm, or blue light exposure before bed.
What time should I sleep to wake at 6am?
For 5 cycles (7.5 hrs), sleep at 10:15 PM. For 6 cycles (9 hrs), sleep at 8:45 PM. Our calculator handles this automatically for any wake time.