Sleep Calculator
Bedtime = Wake time − (Cycle count × 90 min) − 15 min6 cycles: 7:00 − (6×90min+15min) = 7:00 − 9h15min = 9:45 PM
Free online tool
Sleep Calculator
Enter your desired wake-up time or bedtime to find optimal sleep times that align with natural sleep cycles.
Instant calculation
Find Optimal Sleep Times
Enter when you need to wake up or go to bed.
Your result
Calculation
Your numbers stay in this browser. Nothing is uploaded or saved.
Three clear steps
How to use this calculator
- 01
Enter wake-up time
Type the time you need to wake up.
- 02
Calculate
See suggested bedtimes for 4, 5 and 6 sleep cycles.
- 03
Choose a bedtime
Pick a bedtime that gives you complete sleep cycles.
The formula
How this calculation works
Sleep cycles last about 90 minutes. For optimal rest, plan for 5-6 full cycles plus about 15 minutes to fall asleep.
Check the method
Worked examples
Each example follows the same formula used by the calculator.
Need to wake at 7:00 AM — when should I sleep?
6 cycles: 7:00 − (6×90min+15min) = 7:00 − 9h15min = 9:45 PMBedtimes: 9:45 PM (6 cycles), 11:15 PM (5 cycles), 12:45 AM (4 cycles)Common questions
Questions about this calculation
What is the Sleep Calculator?
The Sleep Calculator helps you find the best bedtime or wake-up time based on 90-minute sleep cycles. Enter your values and select Calculate to get an instant result.
How is the result calculated?
Sleep cycles last about 90 minutes. For optimal rest, plan for 5-6 full cycles plus about 15 minutes to fall asleep.
Can you show an example?
Example: Need to wake at 7:00 AM — when should I sleep? — Bedtimes: 9:45 PM (6 cycles), 11:15 PM (5 cycles), 12:45 AM (4 cycles).
Is my data saved when I use the Sleep Calculator?
No. All calculations run locally in your browser. Your inputs and results are never uploaded, stored or shared with anyone.
Is the Sleep Calculator free to use?
Yes. The Sleep Calculator is completely free. No account, sign-up or payment is required. It works on mobile, tablet and desktop.
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