01Why we built this sleep calculator
Have you ever slept a full eight hours and still woken up feeling heavy and foggy? That usually happens when your alarm goes off in the middle of deep sleep. Waking at the end of a sleep cycle often feels very different, even with less total sleep.
Sleep Calculator was built to make that idea simple to use. Pick the time you need to wake up, and the calculator shows you when to fall asleep so you wake up between cycles. No sign-up, no app to install, and nothing to pay.
02What you can do here
Sleep calculator
Find the best bedtime or wake-up time, or see what happens if you go to sleep right now. Try it →
Nap calculator
Plan a 20-minute power nap or a 90-minute full cycle without waking up groggy. Plan a nap →
Sleep debt check
Enter last week's sleep and see how far behind you are, plus a simple plan to catch up. Check now →
Chronotype quiz
Five quick questions to find out whether you're an early bird or a night owl. Take the quiz →
Sleep sounds
Brown, pink and white noise and ocean waves, with a timer that fades out gently. Listen →
Tonight's plan
See when to stop caffeine, put screens away and start winding down for your bedtime.
03How our calculator works
Sleep happens in cycles. Each one moves through light sleep, deep sleep and REM (dream) sleep, and lasts about 90 minutes on average. Most adults need 5 to 6 cycles a night, which is about 7.5 to 9 hours.
When you enter a wake-up time, we count back in full cycles and add the time it usually takes to fall asleep (15 minutes by default). Because everyone is a little different, you can change both the cycle length and the fall-asleep time in the calculator's settings, and choose your age group so results match recommended sleep for your age.
04Where our information comes from
We don't make up sleep advice. Our content is based on widely published guidance from respected health organizations, including:
- Centers for Disease Control and Prevention (CDC): recommended hours of sleep by age
- National Heart, Lung, and Blood Institute (NHLBI): how sleep works and why it matters
- American Academy of Sleep Medicine (AASM): sleep health guidelines
We review our pages regularly. Spotted something that looks wrong? Tell us and we'll check it.
05Our promise to you
- Always free. Every tool on this site is free to use. Ads help us keep it that way.
- Private by design. The tools run in your browser. Your sleep times and answers aren't sent to us.
- No sign-up. Open the page and get your answer in seconds.
- Honest. Our tools are a helpful guide, not a medical device. If you have ongoing sleep problems, we'll always tell you to see a doctor.