Sleep Calculator
Pick the time you need to wake up and get bedtimes that finish a full sleep cycle right at the alarm. Or start from your bedtime and find the best time to set it for.
Go to bed at one of these times
To wake up at 7:00 AM, with about 15 minutes to fall asleep.
Your night
Asleep by about 11:30 PM. Your cycles end around 1:00 AM, 2:30 AM, 4:00 AM, 5:30 AM and 7:00 AM.
Recommended: 7 or more hours a night, from the CDC. Cycles average about 90 minutes but run shorter early in the night and longer toward morning, so treat these times as a good place to start.
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The alarm is set for 6:30 and it is already past 11. Is it worth going to bed now, or will you wake up in the middle of a deep stretch of sleep and feel worse than if you had stayed up a little longer?
This sleep calculator works it out. Sleep runs in cycles of roughly 90 minutes, and waking at the end of one tends to feel easier than being pulled out of the middle. Enter when you need to be up and you get bedtimes that land on the end of a cycle, with the time it takes to fall asleep already allowed for.
Each option is checked against how much sleep the CDC recommends for your age, so a short night gets called a short night.
How the sleep calculator works
Three numbers do the work.
- Cycle length. One trip through light sleep, deep sleep and REM takes about 90 minutes on average. The first cycle of the night is usually 70 to 100 minutes and later ones run 90 to 120, according to the Institute of Medicine's report on sleep. That is why the cycle length is adjustable.
- Time to fall asleep. The calculator allows 15 minutes. A National Sleep Foundation panel rated 15 minutes or less as a sign of good sleep quality at every age, and 16 to 30 as fine too. If you usually lie awake longer, change it.
- How much sleep you need. Adults 18 to 60 are recommended 7 or more hours, so for most people five cycles (7.5 hours) or six (9 hours) is the right answer and four (6 hours) is a short night.
To wake at 6:30 AM after five cycles: five times 90 minutes is 7 hours 30 minutes of sleep, so you need to be asleep by 11:00 PM and in bed by 10:45 PM.
What time should I go to bed?
Find your wake up time and read across. Every bedtime allows 15 minutes to fall asleep.
| Wake up at | 7.5 hours (5 cycles) | 9 hours (6 cycles) | 6 hours (4 cycles) |
|---|---|---|---|
| 5:00 AM | 9:15 PM | 7:45 PM | 10:45 PM |
| 5:30 AM | 9:45 PM | 8:15 PM | 11:15 PM |
| 6:00 AM | 10:15 PM | 8:45 PM | 11:45 PM |
| 6:30 AM | 10:45 PM | 9:15 PM | 12:15 AM |
| 7:00 AM | 11:15 PM | 9:45 PM | 12:45 AM |
| 7:30 AM | 11:45 PM | 10:15 PM | 1:15 AM |
| 8:00 AM | 12:15 AM | 10:45 PM | 1:45 AM |
Six hours is less than the 7 or more recommended for adults. Treat that column as a fallback for a late night, not a plan.
How much sleep do you need?
The CDC's recommendations by age, which draw on the American Academy of Sleep Medicine, the Sleep Research Society and the National Sleep Foundation.
| Age group | Age | Sleep a day |
|---|---|---|
| Newborn | 0 to 3 months | 14 to 17 hours |
| Infant | 4 to 12 months | 12 to 16 hours, including naps |
| Toddler | 1 to 2 years | 11 to 14 hours, including naps |
| Preschool | 3 to 5 years | 10 to 13 hours, including naps |
| School age | 6 to 12 years | 9 to 12 hours |
| Teen | 13 to 17 years | 8 to 10 hours |
| Adult | 18 to 60 years | 7 or more hours |
| Adult | 61 to 64 years | 7 to 9 hours |
| Adult | 65 years and older | 7 to 8 hours |
Source: CDC, About Sleep. The calculator covers ages 6 and up. Younger children's totals include naps, and their sleep cycles are shorter than an adult's.
Can a calculator really time your sleep cycles?
Not to the minute. Cycles are not all the same length, even in one night, and they differ from person to person. Most deep sleep comes in the first third of the night and REM grows longer toward morning, which is part of why early and late cycles feel so different.
What you get is a sensible target. If you wake up groggy at a suggested time, try a cycle length 10 minutes shorter or longer for a few nights and keep whichever feels better.
The bigger win is consistency. The CDC's first tip for better sleep is going to bed and getting up at the same time every day. And if you regularly struggle to fall asleep or stay asleep, that is worth talking to a doctor about rather than calculating around.
More tools
How much sleep you owe this week, and how to pay it back.
A day by day plan for sleep and light around your flight.
A month on one grid, with streaks. Print it if you prefer paper.
How long between two times, including overnight spans.
Questions
What time should I go to bed if I wake up at 6 AM?
For five full sleep cycles, about 7 and a half hours of sleep, be in bed by 10:15 PM. That allows 15 minutes to fall asleep. For six cycles, 9 hours, go to bed at 8:45 PM. Going to bed at 11:45 PM gives four cycles, 6 hours, which is less than the 7 or more hours recommended for adults.
How does a sleep calculator work?
It counts back from your wake up time in sleep cycles of about 90 minutes, then takes off the time it takes to fall asleep. The result is a bedtime that lets you finish a cycle as the alarm goes off, rather than waking partway through one. It works forward the same way from a bedtime.
How many sleep cycles do I need?
Most adults go through 4 to 6 cycles a night. Five cycles is about 7 and a half hours and six is about 9, both within the 7 or more hours the CDC recommends for adults. Four cycles, about 6 hours, falls short.
How long should it take to fall asleep?
Up to about 15 minutes is typical. A National Sleep Foundation expert panel rated 15 minutes or less as a sign of good sleep quality at every age, and 16 to 30 minutes as good too. Regularly taking more than an hour was rated a sign of poor sleep quality, and is worth raising with a doctor.
Is it better to wake up at the end of a sleep cycle?
Usually, yes. Being woken from deep sleep tends to leave people groggy, a state called sleep inertia that can dull thinking for 30 minutes to an hour. Most deep sleep happens early in the night, and cycle lengths vary, so treat cycle timing as a helpful guide rather than an exact science.
Why does the calculator ask for my age?
Because the recommended amount of sleep changes with age. Teens 13 to 17 are recommended 8 to 10 hours, adults 18 to 60 are recommended 7 or more, and adults 65 and older 7 to 8, according to the CDC. The calculator marks each bedtime against the range for the age you pick.
This calculator gives general information built on published averages. It is not medical advice.