How much sleep do you need?

Plenty of people measure their nights against a number, usually eight hours, and either worry about falling short of it or wonder whether the six or so hours that seem to suit them are quietly doing harm. The honest answer sits between a well-supported minimum for most adults and a good deal of variation from one person to the next.

Why the amount varies

Through the day the brain builds up sleep pressure, the drive to sleep, much of it carried by a chemical called adenosine that accumulates the longer you're awake. Sleep is the only thing that clears it. How much sleep you need is, in practical terms, how much it takes to clear that pressure and leave you alert and functioning through the next day. That differs between people and changes across life, which is why the recommendations give a range.

What the expert panels agreed

Two expert reviews set the figures most people quote, and both reached them by panels weighing the published evidence, rather than through one trial.

The American Academy of Sleep Medicine and the Sleep Research Society concluded that adults should sleep seven hours or more a night on a regular basis to promote optimal health (Watson et al., 2015). They added that more than nine hours regularly may be appropriate for young adults, for people recovering from a period of short sleep, and for people who are ill.

The National Sleep Foundation's panel of 18 experts put the appropriate range at seven to nine hours for younger and middle-aged adults and seven to eight for older adults (Hirshkowitz et al., 2015). The panel stated plainly that sleep need varies from person to person, that sleeping outside the range may be appropriate for some, and that straying far from it is rare. The NHS uses the same seven-to-nine-hour range.

We're confident about the floor. Regularly getting less than seven hours is where both panels draw the line for most adults. Where you sit within or above the range is far less certain, and only your own days can tell you.

Time in bed is the chance to sleep

What the panels describe is sleep, and sleep is only part of the time you spend in bed. The rest is falling asleep, waking in the night, and lying there before you get up. Seven hours of sleep usually needs a longer window than seven hours, and how much longer depends on how much of that window turns into sleep.

Our sense of how long we sleep is also less accurate than it feels. Lauderdale and colleagues (2008) compared what 669 middle-aged adults in Chicago said they usually slept with what a wrist monitor recorded over two rounds of three days. People said they slept 6.8 hours on average; the monitor measured 6. The two only moderately agreed, and the shorter someone actually slept, the more they tended to overestimate it. A wrist monitor has its own errors, so this tells us more about the gap between feeling and measurement than about exact minutes.

A short night isn't a diagnosis

A number on its own doesn't tell us whether something's wrong. Six hours chosen because of an early train is a matter of opportunity. Going to bed in good time and still managing only six, night after night, with tiredness and poor concentration during the day, is closer to what the NHS describes as insomnia, which it calls long-term once it has lasted three months or more. And some people genuinely feel and function well near the lower end of the range. We look at the length of the night alongside how you feel the next day before drawing any conclusion.

What your diary adds

Your diary records when you go to bed, how long you take to fall asleep, how long you're awake in the night and when you get up, so we can see both the window and the sleep inside it. If the window is too short, the plan moves lights out earlier in 15-minute steps and watches whether the extra time becomes sleep or time lying awake; if it's the second, we hold the time where it is. Your morning rating of how ready you feel for the day is how we judge whether the sleep you're getting is enough for you.

If you give yourself enough time in bed and still sleep poorly for months, or you nod off during the day without meaning to, see your GP.