Sleep cycle calculator Use 90-minute sleep cycles plus your age to find optimal times. No signup, no ads.
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🛏️ What time should I go to sleep tonight?
We calculate your ideal bedtime tonight from your last wake-up + age-based sleep need.
🌅 What time should I wake up?
We calculate the best wake-up times that land at the end of a 90-min cycle.
How it works
Your brain runs 90-minute sleep cycles through light sleep, deep sleep, and REM. Waking between cycles feels effortless. Waking mid-cycle — especially in deep sleep — leaves you groggy for up to an hour (sleep inertia).
We also add a 15-minute fall-asleep buffer, the average sleep latency for healthy adults.
Sleep needs by age
| Age | Recommended | Cycles |
|---|---|---|
| Toddlers 1–2 | 11–14 hours | consult pediatrician |
| Children 3–5 | 10–13 hours | 7–8 |
| Children 6–12 | 9–11 hours | 6–7 |
| Teens 13–17 | 9–10.5 hours | 6–7 |
| Adults 18–64 | 7–9 hours | 5–6 |
| Older adults 65+ | ~7.5 hours | 5 |
Source: CDC · American Academy of Sleep Medicine
Related calculators
What Is a 90-Minute Sleep Cycle?
A 90-minute sleep cycle is one complete rotation through light sleep (N1, N2), deep sleep (N3), and REM sleep. The 90-minute average comes from foundational research by Dement and Kleitman (1957), who first mapped the rhythmic structure of human sleep.
↑ Back to topHow Many Sleep Cycles Do I Need?
Most adults need 4–6 cycles per night — about 6 to 9 hours. Five cycles (7.5 hours) is the most common sweet spot.
↑ Back to topWhat Happens If I Wake Mid-Cycle?
You hit sleep inertia: 15–30 minutes of grogginess, foggy thinking, and slow reaction times. The fix isn't more coffee — it's timing your alarm to the end of a cycle, which is exactly what this calculator does.
↑ Back to topREM Sleep Explained
REM (Rapid Eye Movement) is the dream-rich stage where the brain is almost as active as when awake. It's essential for memory consolidation, emotional processing, and creativity. REM stretches get longer in the later cycles of the night — which is why a short night robs you of REM disproportionately.
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