Sleep
Is 4 hours of sleep enough?
No, for nearly everyone. Four hours is 3 hours under the 7-hour minimum that US sleep experts set for adults. In a lab study, adults who had four hours in bed for five nights made more slips on an attention test each day, and one long night did not bring them all the way back.
Last updated
Reviewed by Mohammed Raqeeb
The official numbers
How much sleep do experts recommend?
Sleep experts recommend at least 7 hours a night for adults. Two US groups of sleep doctors and researchers set that number together. The CDC, the US public health agency, lists the same number for ages 18 to 60.
A second US health agency, the NHLBI, gives adults a range of 7 to 9 hours. Against that range, a night of 4 hours is 3 to 5 hours short. Teenagers need more, so their gap is bigger.
Teens, 13 to 178 to 10 hours
4 to 6 hours short
Adults, 18 to 607 or more hours
3 or more hours short
Adults, 61 to 647 to 9 hours
3 to 5 hours short
Adults, 65 and older7 to 8 hours
3 to 4 hours short
Hours a night by age, as the CDC lists them.
The research
What did 4 hours of sleep do in a lab study?
Four hours of sleep a night has been tested in a sleep lab. Researchers kept 159 healthy adults there for 12 days (Banks and colleagues, 2010). For 5 nights in a row, most of them were allowed 4 hours in bed, from 4 AM to 8 AM. A smaller group was allowed 10 hours in bed every night.
Every two hours while awake, everyone took an attention test: a signal comes up, and you press a button as fast as you can. A slow press counts as a slip. People also said how sleepy they felt.
Hours in bed each night
4h
142 adults
- Slips on the attention test
- More each day
- How sleepy they said they felt
- Sleepier each day
- After one long night
- Better, but not back to where they began
Hours in bed each night
10h
17 adults
- Slips on the attention test
- No real change
- How sleepy they said they felt
- No real change
- After one long night
- Every night was a long one
Four hours in bed was not four hours of sleep. People slept 3h 43m on the first short night and 3h 51m on the fifth.
After the short nights, some people got one long night, with 10 hours in bed. They slept about nine of them. The next day they did better on the attention test and felt less sleepy. But they were still not back to where they had been before the short nights. The researchers wrote that it may take a longer night, or more than one.
A panel of sleep experts has looked at many studies like this one (Watson and colleagues, 2015). In some of them, six hours in bed gave better test results than four or five. Four hours gave better results than three, two, one or none. So four hours of sleep is better than no sleep, and still well short of enough. For six-hour nights, see is 6 hours of sleep enough.
Feeling fine
Why can 4 hours of sleep feel like enough?
Four hours of sleep can feel like enough because how sleepy you feel is a poor measure of how you are doing. People in the lab study did feel sleepier each day. But the panel of sleep experts found that test scores keep falling the longer short nights go on, and the sleepy feeling does not keep rising in the same way (Watson and colleagues, 2015). So “I feel fine” tells you little about how far behind you are.
Some people believe they were born needing very little sleep. Researchers did find a gene change linked to short sleep, in 2 members of one family (He and colleagues, 2009). Those two people still slept more than six hours a day. The page on five hours of sleep has more on that study.
Try it
What does a week of 4-hour nights add up to?
A week of four-hour nights leaves an adult 21 hours short of the minimum. Each night is 3 hours short, and 7 nights of that make 21. That is as much sleep as 3 full nights. The 5 work nights alone come to 15 hours. Set the counter to your own nights.
Hours short
21h
That is 3h under 7h on each of 7 nights.
3 nights
One block is one night of 7h. The shaded part is sleep you did not get.
This is only a sum of the hours you chose. Nothing you enter leaves this page.
The sleep debt calculator does the same sum from the times you really went to bed and got up.
Not always a choice
When should you see a doctor about short sleep?
Short sleep is not always a choice. The experts who set the 7-hour minimum say that people who worry they sleep too little should talk to their healthcare provider (Watson and colleagues, 2015). The NHLBI says the same.
The CDC says to talk to a provider if you often have problems sleeping. The signs it lists are trouble falling asleep, waking again and again in the night, and feeling tired even after enough sleep. The NHLBI adds loud snoring and breathing that stops and starts. This page reports what studies found. It is not medical advice.
The test
How do you know you are sleeping enough?
You know you are sleeping enough when a written count of your nights says so, because a feeling can be wrong. Each morning, write down when you fell asleep and when you woke up. Count the time asleep, not the time in bed.
If your nights are short because you cannot fall asleep until late, how to fix your sleep schedule moves bedtime earlier a little at a time.
The test
You were asleep for 7 hours or more on at least six nights of the week
for two weeks in a row.
A good way to keep this count takes the hours from what you already write or say about your night, so there is nothing to wear to bed and no timer to start. Most journaling apps only ask how the night felt. They do not show you how many hours it was.
One app built for this is Think in Numbers, a smart journaling app with time tracking built in.
You write or say your day in your own words, as it happens or all at once. The app reads what you wrote and counts the hours that went to each part of it: sleep, your phone in bed, and the time you never mentioned (shown as unaccounted). Then it shows those hours over days and weeks. So you can see, week by week, how many of your nights reached seven hours. Add seven hours of sleep as a daily habit. The app checks it against the hours you wrote, ticks off each night that reaches it, and keeps your streak.
1. You write your day
2. It counts the hours
- Reading in bed0m
- Work0m
- Sleep0m
- Unaccounted24h
3. It shows your week
Reading in bed this week: 0m
On 6 of 7 days. The gap is the day without it.
An example day and week.
For iPhone and Android. Try it on your own day before you pay.
Sources
Where the numbers come from.
Every figure on this page links to one of the papers or official pages below. We checked each one again on .
- Watson and colleagues (2015). Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. J Clin Sleep Med.
- Centers for Disease Control and Prevention (read ). About Sleep.
- National Heart, Lung, and Blood Institute (read ). How Much Sleep Is Enough?
- Banks, S., Van Dongen, H. P. A., Maislin, G. and Dinges, D. F. (2010). Neurobehavioral dynamics following chronic sleep restriction: dose-response effects of one night for recovery. Sleep, 33(8), 1013 to 1026.
- Consensus Conference Panel: Watson, N. F., Badr, M. S., Belenky, G., Bliwise, D. L., Buxton, O. M., Buysse, D. and others (2015). Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult: Methodology and Discussion. Sleep, 38(8), 1161 to 1183.
- He and colleagues (2009). The transcriptional repressor DEC2 regulates sleep length in mammals. Science.
- National Heart, Lung, and Blood Institute (read ). Sleep Apnea: Symptoms.
Keep reading.
- LearnAnswers about sleep, habits, study, people and work, in hours.
- Is 5 hours of sleep enough?What a week of five-hour nights did to people in a lab study, and how much of the lost sleep a weekend makes up.
- Is 6 hours of sleep enough?What the research says, and how to see your real sleep hours.
- Sleep debt calculatorA week of bed and wake times in, hours short out.
- Where did my week go? calculatorEnter a typical day and see your week accounted and unaccounted.
- Time journalingThe method: write or say your day in your own words, then see it as hours.
Questions
Questions people ask.
Is 4 hours of sleep enough for one night?
No. One night of 4 hours leaves an adult 3 hours under the 7-hour minimum. The lab study on this page tested five such nights in a row, and the slips in attention grew each day.
Is 4 hours of sleep better than none?
Yes. In studies that a panel of sleep experts reviewed, four hours of sleep gave better test results than three, two, one or none. Four hours is still 3 hours under the adult minimum.
Can you catch up after a week of 4-hour nights?
Not in one night, in the lab study on this page. After five nights of four hours, people who then had 10 hours in bed did better the next day, but they were not back to where they began.
Is 4 hours of sleep enough for a teenager?
No. The CDC lists 8 to 10 hours for ages 13 to 17. For a teenager, a four-hour night is 4 to 6 hours short.
How can I keep track of how many hours I sleep?
A notebook by the bed works. Each morning, write down when you fell asleep and when you woke up. Look for a way that is easy enough to keep up every morning. One app built for this is Think in Numbers, a smart journaling app with time tracking built in. Think in Numbers counts your hours of sleep from what you write or say about your night, and shows them across the week.
Try it on my day.
Write today down in your own words, and see where the hours went.
For iPhone and Android. Try it on your own day before you pay.