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Sleep Calculator
Plan your sleep schedule around natural 90-minute cycles.
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How to Use This Calculator
- Choose direction — either set a bedtime to find ideal wake times, or set a wake time to find ideal bedtimes.
- Cycles — most adults need 4–6 full cycles (6–9 hours). We add ~15 minutes for falling asleep.
Frequently Asked Questions
How many hours of sleep do I need?
Most adults need 7–9 hours. Children and teens need more, and needs vary by individual.
What are sleep cycles?
Sleep alternates between light, deep and REM stages in ~90-minute cycles through the night. Waking at a cycle boundary feels natural.
Why do I wake up groggy?
You likely woke during deep sleep. Adjusting your wake time to fall at a cycle boundary can help you feel more alert.
How long does it take to fall asleep?
We assume about 15 minutes. Adjust mentally if you usually fall asleep faster or slower.
Practical Example
You need to wake at 6:30 AM and want 5 cycles:
- 5 cycles = 7.5 hours + 15 min to fall asleep = 7h45m.
- Count back from 6:30 AM → bedtime 10:45 PM.
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