Most adults need 7 to 9 hours of sleep per night. The sweet spot for the lowest risk of disease and early death, based on data from four large national studies, falls between 6 and 8 hours. That range holds across age groups, though children and teenagers need significantly more.
Recommended Sleep by Age
Sleep needs change dramatically from birth through old age. For babies and young children, the totals include naps throughout the day.
- Newborns (0 to 3 months): 14 to 17 hours
- Infants (4 to 12 months): 12 to 16 hours
- Toddlers (1 to 2 years): 11 to 14 hours
- Preschoolers (3 to 5 years): 10 to 13 hours
- School-age children (6 to 12 years): 9 to 12 hours
- Teenagers (13 to 18 years): 8 to 10 hours
- Adults (18 to 60 years): 7 or more hours
- Older adults (61 to 64 years): 7 to 9 hours
- Adults 65 and older: 7 to 8 hours
The slight narrowing for older adults reflects real biological shifts. As you age, your body produces less of the hormones that sustain deep sleep, so both total sleep time and the ability to stay asleep tend to decrease. That doesn’t mean older adults need less sleep. It means getting enough becomes harder.
Why Your Body Cycles Through Sleep
Sleep isn’t one uniform state. Your brain moves through repeating cycles that each last roughly 80 to 100 minutes, and a full night typically includes four to six of these cycles. Each one contains lighter sleep stages, deep sleep (when your body does most of its physical repair), and REM sleep (when your brain consolidates memories and processes emotions).
The composition of each cycle shifts as the night goes on. Early cycles are heavier on deep sleep, while cycles closer to morning contain more REM. This is why cutting your night short by even an hour can disproportionately reduce the REM sleep you get, affecting memory, learning, and mood the next day. It also explains why simply “getting a few hours” doesn’t deliver the same benefits as a full night: you’re not just getting less sleep, you’re missing entire types of it.
What Happens When You Sleep Too Little
Consistently sleeping fewer than 6 hours a night raises your risk for several serious conditions. Sleeping just 5 to 6 hours a day doubles the risk of developing prediabetes or type 2 diabetes compared to sleeping 7 to 8 hours. Middle-aged people who sleep under 6 hours and have other sleep problems (like frequent waking) face nearly three times the risk of heart disease. And a large study tracking over 120,000 people with activity monitors found that shorter sleep was consistently linked to higher body mass index.
The risks aren’t only long-term. Sleep loss impairs your reaction time and judgment in ways that are measurable and immediate. Staying awake for 17 hours produces cognitive impairment comparable to a blood alcohol level of 0.05%. At 24 hours without sleep, you’re functioning at the equivalent of 0.10%, which is above the legal driving limit in every U.S. state. A large analysis of the data found that people sleeping 5 hours or fewer had a sharply elevated mortality risk, with a hazard ratio of 2.95 compared to those sleeping the optimal 6 to 8 hours.
Sleeping In on Weekends Doesn’t Fix It
If you regularly cut sleep short during the week and plan to make it up on Saturday, the research is discouraging. A controlled lab study brought healthy adults into a sleep facility for two weeks and compared three groups: one that slept 9 hours nightly, one limited to 5 hours every night, and one that mimicked a common real-world pattern of 5 hours on weekdays with weekend catch-up sleep.
The sleep-deprived group snacked more at night and gained about 3 pounds over two weeks. Their insulin sensitivity, a key marker of metabolic health, dropped 13%. But the weekend recovery group fared even worse on some measures. They gained the same 3 pounds and experienced a 27% decrease in insulin sensitivity. Their liver and muscle insulin sensitivity declined in ways not even seen in the group that was consistently sleep-deprived.
The researchers found that the extra weekend sleep actually disrupted participants’ internal body clocks. When they returned to restricted sleep on Monday, they were more likely to wake at times when their circadian rhythm was still promoting sleep, making the following week’s deprivation feel worse. The lead researcher’s conclusion was blunt: weekend catch-up sleep does not appear to reverse the metabolic damage of chronic sleep loss.
How to Tell If You’re Getting Enough
The number of hours you spend in bed isn’t always the number of hours you actually sleep. A practical way to gauge whether you’re getting enough is to notice how you function during low-stimulation moments. Clinicians use a self-assessment called the Epworth Sleepiness Scale, which asks you to rate your likelihood of dozing off in eight everyday situations: reading, watching TV, sitting in a meeting, riding as a passenger, lying down in the afternoon, sitting and talking with someone, sitting quietly after lunch, and sitting in stopped traffic. You score each from 0 (would never doze) to 3 (high chance of dozing). A total score of 10 or higher suggests you’re not getting adequate sleep.
There are simpler signals too. If you need an alarm clock every single morning and feel groggy for more than 15 to 20 minutes after waking, you’re likely not sleeping enough or not sleeping well. Falling asleep within 5 minutes of lying down is another red flag. It feels efficient, but it typically indicates significant sleep debt rather than good sleep ability. A well-rested person generally takes 10 to 20 minutes to fall asleep.
Finding Your Personal Number
The 7-to-9-hour range for adults is a population average, and your ideal amount sits somewhere specific within it. Genetics, physical activity level, and health conditions all play a role. The most reliable way to find your number is a simple experiment: for two weeks, go to bed early enough to wake without an alarm. After a few days of burning off accumulated sleep debt, you’ll start waking naturally at a consistent time. The difference between when you fall asleep and when you wake is a good approximation of what your body actually needs.
Most people who try this land between 7 and 8.5 hours. Very few adults genuinely function well on 6 hours or fewer. The belief that you can “train” yourself to need less sleep is a persistent one, but sleep researchers have found no evidence that adaptation to short sleep is possible without measurable cognitive costs. What does happen is that people lose the ability to accurately perceive how impaired they are, rating themselves as alert even as their performance on reaction-time and memory tests declines steadily.