Sleep Cycle Calculator
Time your sleep in 90-minute cycles and wake up refreshed.
Sleep runs in ~90-minute cycles; waking mid-cycle causes grogginess. To rise at 6:30 AM feeling fresh, aim to fall asleep at 11:00 PM or 12:30 AM (5 or 4 full cycles) — and allow ~15 minutes to actually fall asleep.
How to use the sleep cycle calculator
- Enter when you must wake up.
- Get ideal bedtimes.
- Or enter bedtime to get wake times.
Sleep Cycle Calculator — FAQs
How long is a sleep cycle?
About 90 minutes: light → deep → REM, repeating. Most adults need 5–6 cycles (7.5–9 hours).
Why do I feel groggy sometimes?
Waking during deep sleep causes sleep inertia — that heavy, disoriented feeling. Waking between cycles avoids it.
Does the 15-minute buffer matter?
Yes — most people need ~15 minutes to fall asleep. Count cycles from sleep onset, not from bed time.
Are naps useful?
A 20-minute nap refreshes without deep sleep; 90 minutes completes a full cycle. Avoid 40–60 minute naps — you’ll wake mid-cycle.
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