Sleep Calculator
Find the best time to go to bed or wake up, so your alarm goes off between sleep cycles instead of in the middle of one.
- 100% free
- No sign-up
- No app
Heading to bed right now? We'll find the best times to wake up.
Adjust: time to fall asleep
Most people take 10 to 20 minutes.
More free sleep tools
SleepTimeCalc has more than just the sleep calculator, and every tool is completely free. No account, no app, no email. Just answers.
- Nap CalculatorWhen to set your alarm for a power nap or a full-cycle nap.
- Sleep Debt CalculatorHow much sleep you owe this week, and how to pay it back.
- Caffeine Cutoff CalculatorHow much caffeine is still in you at bedtime, and your latest cup.
- Sleep Needs by AgeRecommended hours for every age, from newborns to over-65s.
- Sleep Efficiency CalculatorWhat share of your time in bed you actually spend asleep.
- Shift Work Sleep CalculatorWhen to sleep and stop caffeine around any shift, including nights.
- Jet Lag CalculatorDays to adjust, plus a shift-before-you-fly schedule.
How the sleep calculator works
Sleep isn't one long, even block. Through the night, your brain moves through repeating sleep cycles of light sleep, deep sleep and REM (dreaming) sleep. A full cycle takes roughly 90 minutes, and most adults go through four to six a night.
Waking up at the end of a cycle, when you're already in light sleep, usually feels easier than waking up in the middle of deep sleep. That's why 7.5 hours of sleep can sometimes feel better than 8.
The calculator counts backwards (or forwards) in 90-minute steps from the time you give it, and adds about 15 minutes for falling asleep. You can change that under Adjust.
Three ways to use it
- I wake up at: enter your alarm time and get the bedtimes that line up with the end of a cycle.
- I go to bed at: enter when you'll get into bed and get the best times to set your alarm.
- Sleep now: one tap. It uses the current time on your phone.
How many cycles should I aim for?
For most adults, 5 cycles (7.5 hours) or 6 cycles (9 hours) is the target, which is why those are marked Recommended. That lines up with the adult guideline of 7 to 9 hours a night. Four cycles (6 hours) will get you through a short night, but it isn't enough to live on. See how much sleep you need at your age.
Why 90 minutes is an estimate
90 minutes is an average. Real cycles run anywhere from about 70 to 120 minutes, and they change through the night: early cycles have more deep sleep, later ones more REM. So treat the results as good starting points, not exact times. If you keep waking up groggy at one of the suggested times, try the next one along.
Tips to make your results work
- Keep your wake-up time the same every day, weekends included. It anchors your body clock more than anything else.
- Watch the caffeine. An afternoon coffee can still be in your system at bedtime. Check your caffeine cutoff.
- Short on sleep this week? Work out your sleep debt and pay it back gradually.
- Need a boost during the day? Keep naps short. The nap calculator gives you the right alarm time.
Frequently asked questions
What time should I go to bed if I wake up at 6 AM?
For a 6:00 AM alarm, aim for 8:45 PM (6 cycles, 9 hours) or 10:15 PM (5 cycles, 7.5 hours). Both include about 15 minutes to fall asleep. 11:45 PM (4 cycles) works for one short night but is not enough long term.
What time should I go to bed if I wake up at 7 AM?
For a 7:00 AM alarm, try 9:45 PM (6 cycles) or 11:15 PM (5 cycles). Those include about 15 minutes to fall asleep.
Is it better to sleep 6 hours or 7.5 hours?
7.5 hours is better for almost everyone. Both times end on a cycle, so waking up may feel similar, but 6 hours is below the 7-hour minimum adults need, and the shortfall adds up over the week.
How long is a sleep cycle?
About 90 minutes on average, but it ranges from roughly 70 to 120 minutes and varies through the night. The calculator uses 90 minutes as a reliable middle estimate.
Is this sleep calculator free?
Yes. The sleep calculator and every other tool on SleepTimeCalc are completely free, with no account, app or email needed. The calculations run on your own device.
From the blog
- How Many Sleep Cycles Do You Need a Night?Most adults need 5 sleep cycles a night. Here's what happens in each cycle, why the last ones matter, and how to plan your night around them.3 min read
- How Much Caffeine Is in Your Drink? A Chart, Plus Your Cutoff TimeCaffeine in coffee, espresso, tea, soda and energy drinks side by side, plus the latest time to drink each one for a 10:30 PM bedtime.3 min read
- How to Wake Up at 5 AM (Without Feeling Awful)The bedtime you need for a 5 AM alarm, how to shift your schedule without wrecking your week, and the evening habits that make early mornings easier.3 min read
These results are general estimates, not medical advice. Everyone's sleep is a little different. If you're often exhausted despite enough time in bed, snore loudly, or have been told you stop breathing in your sleep, see a doctor.