Sleep Calculator
Find the best time to go to bed or wake up. Enter your wake up time, your bedtime, or sleep now and get times that match the end of a 90 minute sleep cycle.
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Free sleep calculator
A sleep calculator works out when to go to bed or wake up so that you finish a full 90 minute sleep cycle. For most adults, five cycles (7.5 hours) plus about 15 minutes to fall asleep is the target.
Pick what you already know. Set your wake up time to get bedtimes, set a bedtime to get alarm times, or choose sleep now to see when to wake if you lie down this minute. Everything runs in your browser.
What a sleep calculator does
A sleep calculator is a timing tool, not a medical test. It uses one well known pattern: during the night the brain moves through light sleep, deep sleep and REM sleep in a loop that takes about 90 minutes on average. Some people find that waking near the end of a cycle, in lighter sleep, feels easier than being woken from deep sleep, although research on this is limited.
The tool does simple arithmetic. It adds the minutes you need to fall asleep, then counts forward or backward in blocks of 90 minutes. You get a short list of times, and you choose the one that fits your day. The word estimate matters here. Your own cycles can be shorter or longer than that, and they change with age, stress, alcohol and caffeine.
If you want the full method with the sources behind it, read how the times are calculated. For the biology, see what is a sleep cycle.
How to use the sleep calculator
- Choose whether you know your wake up time, your bedtime, or you are going to sleep now.
- Enter the time. The sleep now option reads the clock on your device.
- Set how long you usually take to fall asleep. Fifteen minutes is a common default, but be honest. If you need 30 minutes, choose 30.
- Read the list. Five cycles is the green row and suits most adults. Six cycles suits teenagers and recovery nights. Four cycles is a short night to use only now and then.
- Be in bed and ready at the time shown, with your phone away from your face and the lights low.
Sleep calculator chart: bedtimes by wake up time
This chart is already worked out for the common wake up times. It includes 15 minutes to fall asleep. The first column is when you wake up and the other columns are the matching lights out times.
| Wake up | 6 cycles (9 hours) | 5 cycles (7.5 hours) | 4 cycles (6 hours) |
|---|---|---|---|
| 5:00 AM | 7:45 PM | 9:15 PM | 10:45 PM |
| 5:30 AM | 8:15 PM | 9:45 PM | 11:15 PM |
| 6:00 AM | 8:45 PM | 10:15 PM | 11:45 PM |
| 6:30 AM | 9:15 PM | 10:45 PM | 12:15 AM |
| 7:00 AM | 9:45 PM | 11:15 PM | 12:45 AM |
| 7:30 AM | 10:15 PM | 11:45 PM | 1:15 AM |
| 8:00 AM | 10:45 PM | 12:15 AM | 1:45 AM |
| 9:00 AM | 11:45 PM | 1:15 AM | 2:45 AM |
If your wake up time is not on the chart, use the calculator above. For a full list of single times see the bedtime calculator, and for working forward from lights out use the wake up calculator.
How much sleep do you need
Cycles are only half the story. Total sleep matters too. The American Academy of Sleep Medicine and the Sleep Research Society recommend that adults sleep 7 or more hours a night on a regular basis. Teenagers from 13 to 18 years old need 8 to 10 hours, and school age children from 6 to 12 need 9 to 12 hours, according to the Academy.
| Age | Hours per 24 hours | Typical cycles per night |
|---|---|---|
| Adults, 18 years and over | 7 or more | 5 or more |
| Teenagers, 13 to 18 | 8 to 10 | 5 to 7 |
| School age, 6 to 12 | 9 to 12 | 6 to 8 |
| Preschool, 3 to 5 | 10 to 13 including naps | Naps vary |
| Toddlers, 1 to 2 | 11 to 14 including naps | Naps vary |
| Infants, 4 to 12 months | 12 to 16 including naps | Naps vary |
Use the hours of sleep guide to fine tune this for your own age, and the baby sleep calculator for infants, who do not follow adult 90 minute blocks.
What a sleep calculator cannot do
No calculator can see inside your sleep. It cannot tell you how deeply you slept, whether you have a sleep disorder, or how much sleep your body needs. A few honest limits are worth knowing.
- Cycle length is an average. Your night may run shorter or longer.
- The first cycles of the night have more deep sleep and the later ones have more REM, so cycles are not identical.
- Waking at the end of a cycle may help some people with grogginess, but a regular schedule and enough total sleep matter more than hitting an exact minute.
- Snoring with pauses, gasping, long daytime sleepiness or months of poor sleep deserve a conversation with a doctor.
Make the calculated time work
A bedtime on a screen does nothing until your evening supports it. Keep the same wake up time every day, including weekends, within about an hour. Get daylight early in the day. Keep caffeine well away from bedtime, since a laboratory study found it reduced sleep even when taken 6 hours before bed, and leave a gap of a couple of hours between a large meal and lying down. Dim the lights in the last hour. The sleep hygiene checklist turns these into a short list you can follow.
If you are already behind, the sleep debt calculator shows how much to repay and the nap calculator shows how long a nap should be. If you wake tired even after a full night, read why you wake up tired.
Frequently asked questions
What is a sleep calculator?
A sleep calculator suggests bedtimes or wake up times by counting 90 minute sleep cycles and adding the time you need to fall asleep. It is a planning tool and an estimate, not a medical test.
How do I calculate my sleep?
Count back from your wake up time in blocks of 90 minutes, then subtract about 15 minutes to fall asleep. For a 7:00 AM alarm, five cycles gives a bedtime of 11:15 PM.
How accurate is a sleep calculator?
It is as accurate as the average it uses. Real cycles vary from person to person and night to night, so treat the times as a starting point and adjust by 15 to 20 minutes if you still wake groggy.
How many hours of sleep do I need?
Adults need 7 or more hours, teenagers 8 to 10 hours and school age children 9 to 12 hours, according to American Academy of Sleep Medicine consensus statements.
What time should I go to bed if I wake up at 6 AM?
With 15 minutes to fall asleep, five cycles means lights out at 10:15 PM and six cycles means 8:45 PM. Four cycles means 11:45 PM.
How many hours do teenagers and children need?
CDC guidance lists 8 to 10 hours for ages 13 to 18, 9 to 12 hours for ages 6 to 12, 10 to 13 hours for ages 3 to 5 including naps, and 11 to 14 hours for ages 1 to 2 including naps.
How do I move my bedtime earlier?
Shift it by 15 to 30 minutes every two or three days while keeping the wake time fixed, get bright light after waking and dim lights for an hour before bed.
What happens in one sleep cycle?
A cycle moves through lighter NREM sleep (N1 and N2), deep slow wave sleep (N3) and then REM sleep. Early cycles contain more deep sleep, while later cycles contain more REM, which is why the last hours before waking are valuable for dreaming and memory processing.