Most adults need 7 to 9 hours of sleep per night. The CDC sets the minimum at 7 hours for adults, and consistently sleeping less than that counts as short sleep duration. But the right number shifts significantly depending on your age, and the quality of those hours matters just as much as the quantity.
Recommended Sleep by Age
The National Sleep Foundation convened a panel of sleep experts who established ranges for every stage of life. These aren’t rough estimates. They represent the consensus of researchers who reviewed thousands of studies on how sleep duration affects health at each age.
- Newborns (0 to 3 months): 14 to 17 hours
- Infants (4 to 11 months): 12 to 15 hours
- Toddlers (1 to 2 years): 11 to 14 hours
- Preschoolers (3 to 5 years): 10 to 13 hours
- School-age children (6 to 13 years): 9 to 11 hours
- Teenagers (14 to 17 years): 8 to 10 hours
- Young adults (18 to 25 years): 7 to 9 hours
- Adults (26 to 64 years): 7 to 9 hours
- Older adults (65 and up): 7 to 8 hours
Notice that the range narrows as you age. A teenager genuinely needs up to 10 hours, which is why an adolescent sleeping until noon on weekends isn’t necessarily being lazy. Their biology demands more sleep than an adult’s. Older adults, on the other hand, often find that 7 to 8 hours is the sweet spot, partly because the structure of sleep itself changes with age.
What Happens During Those Hours
Sleep isn’t a single uniform state. Your brain cycles through distinct stages roughly every 80 to 100 minutes. Each cycle includes lighter sleep, deep sleep, and REM sleep (the stage associated with vivid dreaming and memory processing). Over the course of a full night, you’ll complete four to six of these cycles.
Deep sleep is where most physical restoration happens. Your body repairs tissue, strengthens the immune system, and consolidates certain types of memory. Adults should spend about 20 percent of total sleep time in deep sleep, which works out to roughly 60 to 100 minutes during an 8-hour night. The catch is that deep sleep is concentrated in the first half of the night, so cutting your sleep short by even an hour or two disproportionately reduces REM sleep, the stage that dominates later cycles. Both stages serve different functions, and both require a full night to get enough of each.
The Cost of Sleeping Too Little
Sleep deprivation doesn’t just make you tired. It measurably impairs your brain. Being awake for 17 hours straight produces cognitive impairment comparable to a blood alcohol concentration of 0.05%, roughly the equivalent of a couple of drinks. Stay awake for 24 hours and that jumps to the equivalent of 0.10%, which is above the legal driving limit in every U.S. state. Reaction time, decision-making, and emotional regulation all deteriorate in ways that feel invisible from the inside.
The metabolic effects are just as striking. A Stanford study found that people who consistently slept five hours a night had a 14.9 percent increase in ghrelin (the hormone that tells your brain you’re hungry) and a 15.5 percent decrease in leptin (the hormone that signals fullness) compared to people sleeping eight hours. That hormonal shift creates a biological drive to overeat that willpower alone struggles to override.
Chronic short sleep is linked to a long list of serious conditions: heart disease, type 2 diabetes, obesity, depression, and weakened immune function. These aren’t risks that emerge only after years of extreme deprivation. They begin accumulating with regular nights of six hours or less.
The Risks of Sleeping Too Much
Oversleeping carries its own set of problems. Regularly logging more than 9 hours is associated with type 2 diabetes, heart disease, obesity, depression, and headaches. It’s also linked to a greater overall risk of dying from a medical condition. This doesn’t mean that a single lazy Sunday will harm you. The concern is habitual long sleep, night after night.
In many cases, oversleeping is a symptom rather than a cause. If you consistently need more than 9 hours and still feel unrested, that pattern can signal an underlying condition like sleep apnea, depression, or thyroid dysfunction. The excess sleep itself isn’t the root problem, but it’s a signal worth paying attention to.
Why Weekend Catch-Up Doesn’t Work
A common strategy for people who sleep five or six hours on weeknights is to “make up for it” by sleeping in on Saturday and Sunday. Research from Harvard suggests this approach falls short. In one study, subjects who cut their sleep by five hours during the week and then slept extra on weekends still showed excess calorie intake after dinner, reduced energy expenditure, increased weight, and harmful changes in how their bodies processed insulin. Their results were similar to those of people who stayed sleep-deprived all week with no catch-up at all.
Sleep debt, in other words, doesn’t resolve the way a bank overdraft does. You can’t simply deposit extra hours on the weekend and zero out the balance. The metabolic and cognitive damage from short sleep accumulates in ways that extra weekend sleep doesn’t fully reverse. Consistent nightly sleep is far more protective than alternating between deprivation and recovery.
How Screen Time Shifts Your Sleep Window
One of the most common barriers to getting enough sleep is the blue light emitted by phones, tablets, and laptops. Blue light suppresses melatonin, the hormone that signals your brain it’s time to sleep, for about twice as long as other types of light. It also shifts your internal clock by roughly 3 hours, compared to 1.5 hours for green light. That means scrolling through your phone at 10 p.m. can push your body’s natural sleep onset to well past midnight, even if you feel tired.
This doesn’t mean you need to avoid all screens after sunset. But if you’re consistently falling asleep later than you intend and waking up groggy, evening screen exposure is one of the first things worth adjusting. Dimming your screen, using warm-toned display settings, or putting your phone away 30 to 60 minutes before bed can help your melatonin production stay on schedule.
Using Naps to Bridge the Gap
Naps can partially offset a rough night, but length matters. The ideal nap lasts 20 to 40 minutes. That’s long enough to improve alertness and cognitive performance without dropping into deep sleep, which is what causes that heavy, disoriented feeling when you wake up. People who nap longer often wake from a deeper sleep stage and feel worse for 15 to 30 minutes afterward.
A short nap is a useful tool for an occasional bad night, not a substitute for consistently getting your 7 to 9 hours. If you find yourself needing a nap every day just to function, that’s a sign your nighttime sleep isn’t sufficient or isn’t restorative enough.