Most adults need at least 7 hours of sleep per night. The exact number shifts with age, dropping from as much as 17 hours for newborns down to 7 or 8 hours for older adults. But the answer isn’t just about hours on a clock. How much sleep your body actually requires depends on your age, your genetics, and whether the sleep you’re getting is genuinely restorative.
Recommended Sleep by Age
The CDC breaks sleep recommendations into nine age groups, and the ranges are wider than most people expect:
- Newborns (0–3 months): 14–17 hours
- Infants (4–12 months): 12–16 hours, including naps
- Toddlers (1–2 years): 11–14 hours, including naps
- Preschoolers (3–5 years): 10–13 hours, including naps
- School-age children (6–12 years): 9–12 hours
- Teens (13–17 years): 8–10 hours
- Adults (18–60 years): 7 or more hours
- Older adults (61–64 years): 7–9 hours
- Seniors (65+): 7–8 hours
The National Sleep Foundation also recognizes a “young adult” window from 18 to 25, recommending 7 to 9 hours for that group specifically. The CDC’s broader adult category simply says 7 or more, which leaves the upper limit open. In practice, most sleep researchers converge on 7 to 9 hours as the healthy range for the vast majority of adults.
Why Your Brain Needs a Specific Amount
Sleep isn’t passive. While you’re awake, your brain cells burn through energy and produce a byproduct called adenosine. The longer you stay awake, the more adenosine builds up, and the stronger your urge to sleep becomes. This is why you feel progressively groggier during an all-nighter: adenosine is accumulating and pressing down on the brain’s arousal systems like a dimmer switch.
When you finally sleep, your brain clears that adenosine and restores its energy balance. The process takes time. The intensity of your deep sleep in the first few hours is directly proportional to how long you were awake beforehand. If you cut sleep short, you wake up with leftover adenosine still dampening your brain activity, which is why even a “decent” six hours can leave you foggy. Your brain simply didn’t finish its maintenance cycle.
Sleep Quality Matters, Not Just Hours
You cycle through several sleep stages roughly every 90 minutes. Light sleep dominates the early transitions, deep sleep concentrates in the first half of the night, and REM sleep (when most vivid dreaming happens) increases toward morning. Each stage serves a different function. Deep sleep is when the body does its most intensive physical repair and memory consolidation.
Adults should spend about 20% of their total sleep in deep sleep. For an 8-hour night, that works out to roughly 60 to 100 minutes. If you’re getting 7 or 8 hours but waking up exhausted, the problem may not be duration. Alcohol, irregular schedules, sleep apnea, and screen use before bed can all fragment your sleep cycles, reducing the time you spend in deep and REM stages without necessarily waking you up. You log enough hours but miss out on the stages that actually restore you.
Some People Genuinely Need Less
You’ve probably met someone who claims to thrive on five or six hours. Most of them are wrong. They’ve adapted to feeling tired and no longer recognize it. But a small number of people are genuine short sleepers, and the difference is genetic.
In 2009, researchers at UCSF discovered a mutation in a gene called DEC2. People who carry it averaged 6.25 hours of sleep per night, compared to 8.06 hours for people without the mutation. Ten years later, the same team found a second short-sleep gene, ADRB1. This mutation changes the balance of wake-promoting and sleep-promoting brain cells, making carriers easier to rouse and able to stay awake longer without cognitive decline. In mice engineered with the ADRB1 mutation, the ratio of wakefulness-promoting neurons heavily outnumbered sleep-promoting ones.
These mutations are rare. If you need an alarm clock to wake up, feel drowsy by mid-afternoon, or sleep significantly longer on weekends, you are almost certainly not a natural short sleeper. You’re just under-sleeping.
What Happens When You Sleep Too Little
Chronically sleeping under 6 hours carries serious health consequences. Large analyses show a U-shaped relationship between sleep duration and heart disease risk: both very short sleep (under 6 hours) and very long sleep (9 hours or more) are associated with significantly worse cardiovascular health. The sweet spot sits squarely in the 7-to-8-hour range.
In the short term, insufficient sleep impairs reaction time, emotional regulation, and the ability to form new memories. Over weeks and months, it raises blood pressure, disrupts blood sugar control, weakens immune function, and increases appetite hormones that drive weight gain. The effects are cumulative. A week of sleeping 6 hours a night produces cognitive impairment equivalent to staying awake for 48 hours straight, even though you may feel like you’re functioning normally. That gap between how impaired you are and how impaired you feel is one of sleep deprivation’s most dangerous features.
One simple way to gauge whether you’re getting enough sleep: think about how likely you are to doze off during quiet activities like reading, watching TV, or sitting in a meeting. Clinicians use a tool called the Epworth Sleepiness Scale, which scores your dozing likelihood across eight everyday scenarios on a 0-to-3 scale. A total score above 11 (out of 24) suggests you’re not getting adequate sleep and may benefit from evaluation. You can find the questionnaire online and score yourself in about two minutes.
Can You Sleep Too Much?
Regularly needing more than 8 or 9 hours and still feeling unrested is a signal worth paying attention to. Oversleeping itself hasn’t been proven to cause disease, but it frequently accompanies conditions like depression, diabetes, heart disease, and sleep disorders such as apnea. The long sleep isn’t the problem. It’s often a symptom of something else preventing restful sleep or draining your energy.
If you consistently sleep 9 or more hours and still don’t feel refreshed, that pattern is worth investigating. The goal isn’t to force yourself to sleep less. It’s to figure out why the sleep you’re getting isn’t doing its job.
Finding Your Personal Number
The best way to determine your ideal sleep duration is a simple experiment. Choose a week when you don’t have early obligations. Go to bed when you feel genuinely sleepy and wake up without an alarm. By the third or fourth day, after you’ve paid off any accumulated sleep debt, the number of hours you naturally sleep is a good approximation of what your body actually needs.
Most people land between 7 and 9 hours. If your result is consistently under 7, pay attention to how you feel during the day. True sufficiency means no afternoon drowsiness, no difficulty concentrating, and no urge to “catch up” on weekends. If any of those are present, your body is telling you it needs more, regardless of what the clock says.