We’ve all heard adults should aim to get seven to nine hours of sleep per night. (Younger teens and children generally need more.) It’s probably the number that you think about when tossing and turning with insomnia, wondering if you’ll ever get to sleep or if you can survive the next day on fewer hours. This “ideal number” comes from a variety of sources and studies, including an expert panel from the National Sleep Foundation, which looked at the existing research on the subject. In general, it’s become the be-all and end-all of sleeping hours.
However, some people may need more sleep and some people may need less. Getting seven to nine hours of sleep each night is a recommendation that covers most adults, but the NSF also recognizes that both six hours and 10 hours “may be appropriate” too. According to a 2015 study in the journal Sleep Health: Journal of the National Sleep Foundation, the requirements for getting an adequate amount of sleep will vary across the lifespan and from person to person. For example, newborns, infants, and toddlers need 12 to 18 hours of sleep daily; older children need 11 to 13 hours; teenagers (ages 14 to 17) need 8 to 10 hours; while older adults (65+) need 7 to 8 hours, according to the NSF.
So, how do we know how much sleep do we exactly need?
The “magic number” of hours of sleep
“Everyone kind of focuses on eight hours, because it’s in between the seven to nine recommended amount. But the reality is around 70 percent of people need that, and then there are outliers,” says Shelby Harris, PsyD, a clinical psychologist in White Plains, New York and a clinical associate professor in the departments of neurology and psychiatry at the Albert Einstein College of Medicine in Bronx, New York. “There are some people that actually need less and are fine and there are some people who need more,” Dr. Harris says.
So, how do you know what’s right for you? It really just depends on how you feel. According to Dr. Harris, “If you’re getting the same amount on a daily basis and feel well rested and refreshed to go about most of the day, then that’s your magic number.” Science also agrees. A 2018 study in the journal Nature and Science of Sleep suggests there is no “magic number” for the ideal duration of sleep and these needs vary by individual. (If you don’t have a consistent sleep schedule, or are doing other things that interfere with sleep, like drinking alcohol before bed, you won’t be able to tell if you’re feeling tired because you need more sleep or because you need to fix your sleep habits.)
When you need more sleep than “normal”
Alcibiades J. Rodriguez, MD, an assistant professor of neurology and the director of the Comprehensive Epilepsy Center-Sleep Center at NYU Langone Health in New York, says that some people who tend to need more hours of sleep than normal may actually have an undiagnosed medical problem. “Many people find out later in life there’s something else going on, like sleep apnea,” Dr. Rodriguez says. Sleep apnea is a condition in which the airway collapses during sleep, causing episodes—sometimes dozens of times a night—where you snort and gasp for breath. One symptom of sleep apnea is snoring, and the condition can leave you feeling exhausted without ever being aware you have it. (Here’s what doctors wish you knew about snoring.)
He also notes that on the other side of the spectrum, very type A people may swear they only need five or six hours of shut-eye, and people with high IQs can operate at less than 100 percent of their capacity and still seem to be fine because they’re still high performing comparatively, Dr. Rodriguez says.
But just because you can force yourself to run off little sleep doesn’t mean that you’re getting the sleep you need. Skimping on sleep can have effects beyond interrupting productivity and making us moody. Long-term, sleep deprivation can have negative effects on heart health, metabolism and weight, skin health, and immune health.
Genetics influence sleep needs
There’s a wide range when we talk about what’s normal, and how much sleep you need to feel rested comes down to individual genetic variations, says Dr. Harris. “There’s no way to adjust it. Sleep is a necessary biological function that your body has at a set point, and that’s what you have to go with.”
Of course, you can probably run off less sleep than you actually need—we’ve all done it before and will do it again—but you’ll feel the effects eventually, and it’s not going to get easier for your body to muscle through. (Hello, burnout.) Same thing on the other end: You can try all you want, but if you only need six hours of sleep, good luck trying to force yourself to stay in bed for nine or 10.
Sudden changes in sleep needs may signify a problem
Any sudden change in how rested you feel can indicate a sleep disorder, says Dr. Rodriguez. “In general, if your performance at work or school changes, you experience decreased attention or concentration, an increase in irritability, or any other type of change in sleepiness, that may indicate something is not right.”
On the flip side, if you always felt like you needed eight hours of sleep, but now suddenly need nine or 10 to feel rested, something may have changed. Sleep disorders like obstructive sleep apnea or restless leg syndrome can cause you to get less restful sleep and leave you feeling zonked with your normal sleep schedule. (Here are seven sleep disorders that can keep you awake.
DGLimages/Getty ImagesUse of alarm clocks can be a sign of a sleep problem
Frequent snoozers, this one’s for you. “If somebody needs an alarm clock every single morning to wake up, that’s not normal,” Dr. Rodriguez says. “That’s an indication you need more sleep or that your sleep quality is impaired. It could be a sign of a sleep disorder.” If you consistently wake up naturally after a certain number of hours, you’re likely getting the sleep your body needs, whether it’s six hours or 10 hours. But if your internal alarm clock seems to be missing altogether, such as you could sleep all day long if you let yourself, it’s time to take a hard look at your sleep habits and figure out what’s going on.
Sleep quality over quantity
Most doctors would agree that it’s better to get less high-quality sleep than more crummy sleep. “If you’re getting 10 hours but it’s broken and you’re waking up all night from snoring, I’d rather you get six hours of better quality sleep,” says Dr. Harris. If you don’t feel like you’re sleeping long enough, first look at the quality of your sleep—are you practicing good sleep habits? Are you drinking alcohol before bed? Do you sleep through the night or do you wake up often? Does your partner tell you you snore or kick or steal all the covers? Do an audit and make some changes in the quality category first, and then work on lengthening the time if you still feel like you need it. (Here are the little changes to make for better sleep.)
Talk to your doctor about your sleep habits
If you’re sleeping a ton but are still exhausted during the day, or sleep very little and want to figure out how to catch more quality zzz’s, Dr. Rodriguez suggests seeing your primary care doctor first. They can help rule out a handful of medical conditions unrelated to sleep that could be making you lethargic—everything from anemia to a thyroid condition can impact how tired you feel during the day. If there doesn’t seem to be a pervasive medical issue, the next step is looking into your sleep quality and if a sleep disorder, like insomnia, may be lurking and messing with your body clock. (Here are some remedies for insomnia.)