Sleep Calculator — Best Time to Sleep & Wake
Waking in the middle of a sleep cycle leaves you groggy. Enter when you need to wake up (or when you're going to bed) to get times that line up with complete cycles.
Updated
For general information only — not medical advice. Consult a doctor or registered dietitian before making health decisions.
Formula
Bedtime = Wake time − (cycles × 90 min) − time to fall asleep
Each sleep cycle lasts about 90 minutes. Five or six cycles (7.5–9 hours) suits most adults.
Examples
Wake at 6:30 AM
To wake at 6:30 AM, go to bed at 9:15 PM or 10:45 PM
Bed at 11:30 PM
If you go to bed at 11:30 PM, wake up at 7:15 AM or 8:45 AM
Important information
- Cycle length varies from about 80 to 110 minutes between people — adjust by 15 minutes if you still wake groggy.
Frequently asked questions
How many hours of sleep do I need?
Adults need 7–9 hours; teenagers 8–10 hours.
Why do I feel tired after 8 hours?
You may be waking mid-cycle. Try 7.5 or 9 hours instead.
How long does it take to fall asleep?
Around 10–20 minutes for most people.
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