How many hours of sleep do you need?

How many hours of sleep does an adult need?

The best-known answers come from professional organizations. An expert panel convened by the US National Sleep Foundation set out recommendations by age [1]:

The American Academy of Sleep Medicine and the Sleep Research Society reached a similar conclusion: adults should regularly sleep 7 hours or more. More than 9 hours may be appropriate for young adults, for people catching up on lost sleep and during illness [2].

The National Sleep Foundation panel adds a caveat. These numbers apply to healthy people without sleep disorders, and needs differ from person to person. Sleeping outside the range can be fine, but straying far from it is rare. If you routinely sleep much less or much more, it’s worth getting your health checked [1].

Plenty of people feel they fall short. In a Gallup poll of 1,013 US adults in December 2023, 57% said they would feel better with more sleep, and 20% reported getting five hours or less [3].

What the Nature study found

In May 2026, the journal Nature published a study based on UK Biobank data from people aged 37 to 84 [4]. Participants were asked roughly how many hours they sleep in every 24 hours, naps included.

Researchers compared those answers with 23 “aging clocks.” These are models that estimate the biological age of organs from MRI scans and from proteins and metabolites in the blood. The difference between biological age and actual age is called the biological age gap.

A significant U-shaped pattern appeared for 9 of the 23 clocks. U-shaped means the results were worse with both short and long sleep and best somewhere in the middle.

Why there’s no single number

The low point shifts even for one organ. Judged by blood proteins, the brain showed the lowest aging burden at about 7.7 hours. Judged by MRI, it was closer to 6.5 hours [4].

Across the nine significant measures, the low points ranged from 6.5 to 7.8 hours in women and from 6.4 to 7.7 hours in men. The authors treated 6–8 hours as normal for their analysis, and they point out that studies define normal sleep in different ways.

What if you sleep less than 6 or more than 8 hours?

Compared with the 6–8 hour group, the risk of death from any cause was higher at both ends [4]:

Short sleep was also linked to depressive episodes, anxiety disorders and primary insomnia. Long sleep is harder to interpret. The authors suggest it may not be a direct risk factor at all, but rather a sign that the body is compensating for something or that an illness hasn’t surfaced yet. So sleeping nine hours is no reason to panic.

What this study doesn’t prove

• Its design limits what it can say about cause and the direction of the effect.
• Sleep duration came from questionnaires, so people may have misremembered.
• Participants were mostly of European ancestry.
• Circadian misalignment and broken sleep weren’t directly measured.

So it doesn’t show that six and a half hours is enough for everyone, or that sleeping more than eight is dangerous.

Regularity: what the hours don’t tell you

A separate UK Biobank study tracked the sleep of 60,977 people with accelerometers instead of relying on questionnaires. People with more regular sleep had a 20–48% lower risk of death from any cause than the least regular group, and regularity predicted that risk more strongly than duration did [5]. This is an observation too, not proof of cause, but it may help explain why the same seven hours can feel so different from one week to the next. For a place to start, see how to fix your sleep schedule.

How to figure out how much sleep you need

You’ll find your number faster by testing it than by reading a table. Give it a week or two.

1. Pick a wake-up time and keep it every day, weekends included.
2. Go to bed when you feel sleepy. Don’t turn in early to rack up hours: lying awake in bed tends to do more harm than good [6].
3. Answer three questions each morning: What time did you fall asleep? How many times did you wake up during the night? What was your energy level on waking, on a scale of 1–10?
4. Judge by your day, not the number. If you have energy in the morning and don’t feel drowsy during the day, that amount of sleep is working for you.

Sleep Reset starts from the same idea: how you feel counts more than any device metrics. Two signs to look for are falling asleep within 15–20 minutes and waking up energized and clear-headed. If you’re waking up during the night, read why it happens around 3am.