How many calories do you burn while sleeping?

Your body does not switch off when you fall asleep. Your heart keeps beating, your lungs keep breathing, your brain sorts through the day's memories, your liver and kidneys keep working and your cells keep renewing themselves. All of that invisible activity has an energy cost, which researchers call the sleeping metabolic rate.

To measure it, volunteers sleep inside a room calorimeter: a sealed room where the oxygen they consume and the carbon dioxide they breathe out are analysed around the clock. In 1988, a team in Cambridge used this method to compare the overnight energy use and the basal metabolic rate of 80 adults. Across the whole night, expenditure averaged 95% of basal metabolic rate, dropping to about 88% during the calmest stretch of sleep. A 2004 Japanese study of 94 adults found the same average ratio of 0.95, with real differences from one person to the next.

In practice, an hour of sleep costs only slightly less than an hour lying awake in bed on an empty stomach. Sleep is not a dramatic energy-saving mode: it lowers expenditure by roughly 5%, not by half. That is why the best way to estimate the calories you burn overnight is to start from your basal metabolic rate.

Body weight is the biggest factor, simply because a heavier body has more tissue to maintain. The chart below starts from the weight-only version of the Mifflin-St Jeor equation (resting expenditure = 15.1 × weight in kg + 371), developed in 1990 from 498 adults, then applies the 0.95 ratio measured during sleep.

So a 70 kg (154 lb) adult burns about 450 kcal in 8 hours, and a 100 kg (220 lb) adult close to 600 kcal. Put another way, you burn between 0.7 and 0.9 kcal per kilogram per hour while you sleep, or roughly 0.3 to 0.4 kcal per pound. The figure per kilogram falls slightly as weight goes up, because fat tissue uses less energy than muscle and organs.

Now zoom out to 24 hours. Your basal metabolic rate (BMR) is the energy you use at complete rest, fasted, at a comfortable temperature. It is the foundation of your daily expenditure, and for most adults it outweighs exercise by a wide margin. The full Mifflin-St Jeor equation is the most widely used way to estimate it: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then + 5 for men or − 161 for women.

Of course, nobody spends the day motionless in bed. Getting up, showering, cooking and walking to the bus all add up. Experts from the FAO, WHO and UNU class a lifestyle as "sedentary or lightly active" when total expenditure is 1.4 to 1.7 times BMR. A desk-bound day with no exercise sits near the bottom of that range, which gives your total daily energy expenditure (TDEE). Here is what that looks like for a few typical profiles.

Two people of the same weight do not burn the same amount while they sleep. Six factors explain most of the difference, but none of them changes the picture by more than a few dozen calories a night.

Yes and no. Every night you draw on your energy stores, and the scale often shows a little less in the morning than it did the night before. But most of that difference is water lost through breathing and sweating. A 450 kcal night is equivalent, on paper, to around 50 grams of fat, and only if your whole day is in deficit.

Sleeping longer does not burn more either, since an hour asleep costs slightly less than an hour awake. A University of Colorado team measured this in 2011: during a night of total sleep deprivation, overnight expenditure rose by about 32%, and 24-hour expenditure by about 7%. In 2013, the same team found that five short nights increased daily expenditure by about 5%, yet led to an average weight gain of 0.8 kg (1.8 lb), because participants ate far more than that small extra burn, especially in the evening after dinner.

That is the paradox: staying awake burns a few more calories, but your brain asks for many more in return. The real link between sleep and weight is all about appetite.

In 2004, a University of Chicago team restricted the sleep of twelve healthy young men for two nights, with identical meals and activity. Leptin, the hormone that signals fullness, fell by 18%; ghrelin, which drives appetite, rose by 28%; and self-rated hunger went up by 24%, with a clear pull towards carbohydrate-rich foods. That same year, data from more than 1,000 participants in the Wisconsin Sleep Cohort showed the same pattern in short sleepers: 15.5% less leptin and 14.9% more ghrelin with 5 hours of sleep instead of 8.

Those hormones show up on the plate. In 2017, a King's College London meta-analysis pooled trials that cut volunteers' sleep: after shortened nights, they ate an average of 385 kcal more per day, without burning any more. Most of the surplus came from fat. Over a week, that is close to 2,700 kcal, enough to explain much of the link between sleep and weight seen in population studies.

It works the other way too. In a trial published in JAMA Internal Medicine in 2022, adults with overweight who slept less than 6.5 hours a night received simple advice on extending their sleep. They gained about 1.2 hours of sleep a night, and their intake fell by about 270 kcal a day compared with the control group, with no diet imposed. That is the range to remember: a night that is too short often means 250 to 400 extra calories the next day.

Sleep does not only affect how much you eat; it also shapes what kind of weight you lose. In 2010, Chicago researchers followed ten adults with overweight through two 14-day periods on the same reduced-calorie diet, one with 8.5 hours in bed and the other with 5.5 hours. With short nights, the share of weight lost as fat fell by 55% (0.6 kg versus 1.4 kg), and the loss of fat-free mass rose by 60%. Participants also felt hungrier.

It is a small study, but its message fits with the rest: short sleep pushes the body to hold on to fat and draw on muscle, the very tissue that keeps your basal metabolic rate up. Chronic sleep loss can therefore slow down a well-designed diet, even when calories are perfectly under control.

The official benchmark is simple: the US National Institutes of Health recommend that adults sleep 7 to 9 hours a night. If you fall short, gaining even one extra hour may be one of the most underrated levers for your weight.

While you sleep, your body burns about 95% of your basal metabolic rate, or 400 to 600 kcal a night for most adults: real expenditure, but not something you can meaningfully increase. Weight, muscle mass, age and sex move that figure by a few dozen calories, not a few hundred. The real issue lies elsewhere, because nights that are too short make you eat 250 to 400 extra calories the next day and steer weight loss towards muscle rather than fat. Protecting 7 to 9 hours of sleep remains one of the simplest and most rewarding things you can do for your weight, long before any trick to burn more calories in your sleep.