Sleep Calculator
Runs on your device. Nothing is sent.Nothing is uploaded - the times are worked out in your browser.
Go to bed at one of these times
- 9:45 PM9 h6 cyclesRecommended
- 11:15 PM7 h 30 min5 cyclesRecommended
- 12:45 AM6 h4 cycles
- 2:15 AM4 h 30 min3 cycles
Includes 15 minutes to fall asleep.
Adjust to you
7-9 hours of sleep a day are recommended at this age.
Find the best time to go to bed or wake up, counted in 90-minute sleep cycles so the alarm rings between cycles, not in deep sleep.
Sleep runs in cycles of roughly 90 minutes: light sleep, deep sleep, then dreaming (REM). Waking at the end of a cycle usually feels easier than being pulled out of deep sleep halfway through. Tell the calculator when you need to get up and it counts back whole cycles, plus the time it takes you to fall asleep, to give you bedtimes. Or tell it when you're going to bed and it gives you alarm times. Times that match the hours recommended for your age are marked. Nothing is sent anywhere.
Frequently asked questions
Why 90 minutes?
One pass through light sleep, deep sleep and REM takes about 90 minutes in most adults, usually somewhere between 80 and 110. If you often wake just before the alarm or feel groggy at the times shown, try a slightly shorter or longer cycle in the settings.
How many cycles do I need?
Most adults need 7 to 9 hours, which is five or six cycles. Four cycles (6 hours) is fine now and then but not every night. Teenagers need 8 to 10 hours and school-age children 9 to 11.
What does the time to fall asleep do?
Cycles start once you are asleep, not when you lie down. Most people take 10 to 20 minutes to drift off, so the calculator adds 15 minutes by default. Change it if you usually fall asleep faster or take longer.
Is this medical advice?
No. It's a rule of thumb based on average sleep cycles. If you are tired however long you sleep, snore loudly or wake up often, talk to a doctor.