About the Sleep Calculator
Find the best bedtime for the time you need to wake up. This tool is free, works in your browser and needs no sign-up.
How to use the Sleep Calculator
Pick your wake-up time. The tool counts back in 90-minute sleep cycles and adds 15 minutes to fall asleep.
Formula used
Bedtime = Wake-up time − (cycles × 90 minutes) − 15 minutes.
Example
With Wake-up time 07:00, the calculator shows: 6 cycles (9 hours) = Go to bed at 21:45; 5 cycles (7.5 hours) = Go to bed at 23:15; 4 cycles (6 hours) = Go to bed at 00:45.
Frequently asked questions
Is the Sleep Calculator free to use?
Yes. It is completely free and you can use it as many times as you like.
How accurate is the Sleep Calculator?
The calculator uses standard formulas, so the maths is exact. Real life results can differ because of fees, taxes, rounding or personal factors, so treat the answer as an estimate.
Do you store the numbers I enter?
No. All calculations run in your browser. The values you type are not sent to our server.
Disclaimer: results are estimates for information only. They are not financial, medical or professional advice.