Is 6 Hours of Sleep Enough? (And What About 5 or 7?)

For most adults, 6 hours of sleep a night is not enough. Sleep experts recommend 7 or more hours on a regular basis, and getting less than that is linked to health problems ^[1]. Five hours is clearly too little for almost everyone, while 7 meets the minimum. The tricky part is that a 6-hour habit can feel normal even while it slows you down.

The short answer for 5, 6 and 7 hours

The American Academy of Sleep Medicine and the Sleep Research Society set the bar at 7 hours for adults, and say that sleeping less than 7 hours on a regular basis is associated with weight gain, diabetes, heart disease, depression and a higher risk of death ^[1]. These are associations from population studies, not a promise that every short sleeper will get sick. But they point the same way as the lab evidence below.

A single 6-hour night is not the issue. The question is what you do night after night. If you like to think in cycles, 6 hours is about four of them, and our page on how many sleep cycles you need shows how that compares with the usual five.

What two weeks of 6-hour nights does

The clearest evidence comes from a lab study in which 48 healthy adults aged 21 to 38 were randomly assigned to 4, 6 or 8 hours in bed for 14 nights in a row, while another group went without sleep for three nights ^[2]. Researchers tested them regularly on attention and thinking tasks.

In the 6-hour and 4-hour groups, performance slipped further day after day. By the end of the two weeks, the authors judged that nights of 6 hours or less had left people as impaired as up to two nights with no sleep at all ^[2]. Six hours in bed, remember, means a little less than 6 hours of actual sleep.

A statistical model from the same study found that lapses in attention rose almost in a straight line with the total time spent awake beyond about 16 hours a day, whether that extra time came from short nights or from no sleep at all ^[2]. The authors described sleep debt as extra wakefulness whose cost builds up over time ^[2].

Why you may not feel impaired

If 6 hours is so costly, why do so many people say they feel fine on it? The same study has an answer. Volunteers' own sleepiness ratings jumped in the first days and then barely rose, even as their test performance kept sliding. The 6-hour and 4-hour groups did not even rate themselves very differently ^[2]. In the researchers' words, the volunteers were largely unaware of their growing deficits ^[2].

This matters most on the road. Drowsy driving is behind serious crashes, injuries and deaths ^[8], and your own sense of alertness is not a reliable gauge after a run of short nights. If you feel drowsy, do not drive. And the idea that you can teach yourself to need less sleep without any downside is, according to the National Heart, Lung, and Blood Institute, a common myth ^[8].

Short sleepers: the rare exception

There really are people who thrive on less. Sleep doctors describe "short sleepers" who regularly feel alert and refreshed after less than 6 hours, have no trouble sleeping and do not try to catch up on weekends or holidays ^[5]. In one small family, scientists found a gene mutation linked to naturally short sleep ^[6], and research suggests that true short sleepers may carry mutations that let them function well on less sleep ^[5].

But they are a small minority. Many people sleep under 6 hours without being short sleepers. They are simply restricting their sleep, which shows up as naps and long weekend lie-ins ^[5]. A simple test: if you sleep much longer whenever you get the chance, you are probably not a natural short sleeper.

Teens and older adults

The 7-hour minimum is for adults. Teenagers aged 13 to 18 are advised to sleep 8 to 10 hours a day ^[3], so 6 hours leaves them even further behind.

At the other end of life, people often assume they need less sleep. Older adults actually need about the same as other adults, around 7 to 9 hours, but they tend to go to bed and get up earlier, and their sleep becomes lighter with more wake-ups ^[7]. The National Sleep Foundation's panel suggested 7 to 8 hours for adults over 65 ^[4]. Waking at 5 a.m. after going to bed at 11 is a short night at any age.

How to tell if your number is enough

Recommended ranges describe most people, and the National Sleep Foundation's experts note that a duration a little outside the range may be appropriate for some, while straying far from it is rare ^[4]. So how do you find out where you fit? Picture a normal week. If you can't wake without an alarm and still feel groggy well after the first half hour, if you nod off in meetings or as a passenger, or if you sleep 2 or more hours longer on days off, you are probably short. The most telling sign is that you feel better when you do get more sleep, which is one of the things sleep doctors look for in insufficient sleep ^[9].

The simplest experiment is to go to bed 30 minutes earlier for two weeks and keep your wake time fixed. If your afternoons get easier, your old number was too low. Our sleep need calculator gives you a starting range by age, and the sleep debt calculator shows how quickly short nights add up. If you are sleeping well past 9 hours instead, see whether 9 hours is too much.