Sleep calculator
Find the best time to go to bed or wake up based on 90-minute sleep cycles.
When should I sleep or wake up?
Everything happens on your device: nothing is uploaded to the internet.
Available in: 
Sleep calculator: what it is for
The calculator uses sleep cycles of about 90 minutes to suggest bedtimes or wake-up times at the end of a cycle, when it's easier to get up. It already allows about 15 minutes to fall asleep.
Choose the time you want to wake up, the time you'll go to bed, or sleep now.
How to use
- Choose wake up at, go to bed at or sleep now.
- Enter the time.
- See the best times, with 5 or 6 cycles highlighted.
When to use it
- Wake up less tired.
- Plan the night before an exam or a trip.
- Adjust your sleep routine.
Frequently asked questions
Why 90-minute cycles?
Sleep goes through stages that repeat in cycles of about 90 minutes. Waking up at the end of a cycle, and not in the middle of deep sleep, helps you wake up feeling better.
How many cycles should I sleep?
Adults usually need 5 to 6 cycles (7.5 to 9 hours). The calculator already allows about 15 minutes to fall asleep.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.