How many hours of sleep do I actually need?

Two major expert reviews landed on almost the same answer in 2015. The National Sleep Foundation convened an 18-member panel representing twelve organisations to weigh the accumulated literature, and recommends 7–9 hours per night for adults and 7–8 hours for older adults. The same year, the American Academy of Sleep Medicine and the Sleep Research Society stated in a joint consensus that adults should sleep at least 7 hours per night on a regular basis.

Their review links regularly sleeping less than 7 hours to weight gain and obesity, diabetes, high blood pressure, cardiovascular disease, depression and increased mortality, as well as to impaired immune function, worse performance and more errors. More than 9 hours may be reasonable for young adults, for people paying off a sleep debt, or for those who are ill; for everyone else, it is uncertain whether long sleep in itself carries any risk.

For anyone counting calories there is an unusually concrete number. When Al Khatib and colleagues pooled eleven experimental studies, participants ate on average 385 kcal more per day after partial sleep deprivation compared with normal sleep, with no increase in energy expenditure. The lost sleep did not turn into extra burn; it turned into a plain energy surplus, with more fat and less protein on the plate.

Needs vary within the 7–9 range, and both panels acknowledge that exceptions exist. But they are equally clear that people who genuinely thrive far outside the range are rare. The odds that you are a true exception are small.

Part of why exactly "8 hours" has stuck is that round numbers are easy to remember: the middle of the 7–9 range became the rule, and the rule became a requirement. The misunderstanding also runs the other way. Hustle culture has long rewarded people who get by on little sleep, and someone bragging about five hours reads as efficient rather than impaired. That works because chronic sleep restriction blunts precisely the ability to judge how impaired you are; you get used to the feeling, not the consequences. Meanwhile an industry of sleep apps, trackers and mattresses profits from turning sleep into yet another performance metric. A perfect sleep score sells better than the undramatic news that 7–9 hours is enough.

Aim for 7–9 hours and find your level within the range: you should be able to wake up rested without sleeping away half the weekend. Give yourself a sleep window that actually fits it, including time to fall asleep. If you count calories, sleep is part of the budget; in the pooled studies participants ate on average about 385 kcal more after short nights, so an earlier night is often a better tool than more willpower the next day. If you consistently sleep poorly despite making room for it, that is a question for a healthcare professional, not for more apps.