The short answer: Most adults burn roughly as many calories per hour asleep as their basal metabolic rate, or slightly fewer. In whole-body calorimeter studies, overnight energy use averaged 95% of basal metabolic rate in lean adults. For a 40-year-old woman who weighs 70 kg, the Mifflin-St Jeor equation puts that near 430 to 460 calories over 8 hours. Body size sets most of the number, and sleep stage changes it very little.
How does sleeping metabolic rate compare with BMR?
Basal metabolic rate (BMR) is the energy you use awake, lying still, fasted, in a comfortable room. Sleeping metabolic rate is the energy you use while asleep. The two are close, but they are not the same measurement.
A British team tested this in 80 healthy people measured on 246 occasions by whole-body calorimetry. In 40 lean adults, the overnight rate averaged 0.95 of BMR, with a range of 0.85 to 1.02. The lowest point of the night averaged 0.88 of BMR. The authors concluded that using BMR for the sleep hours overestimates by about 5 percent on average.
A later Dutch study found the gap depends on age. In 30 young adults, the overnight-to-BMR ratio averaged 1.00. It averaged 0.92 in children and 1.06 in adults around age 61. For most adults, BMR is a fair stand-in for a night of sleep.
Sleep still saves energy compared with staying awake. In a small calorimeter study of seven young adults, night-time energy use rose by about 32% when they stayed awake all night.
How do you estimate a night's calorie burn?
Start with a resting energy equation, then scale it to the hours you sleep. The Mifflin-St Jeor equation was published in the American Journal of Clinical Nutrition in 1990. It came from indirect calorimetry in 498 healthy adults aged 19 to 78. Strictly, it predicts resting energy expenditure, which is close to BMR.
- Men: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5
- Women: (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161
Here is the arithmetic for a 40-year-old woman who weighs 70 kg and is 165 cm tall:
- Resting energy: 700 + 1,031 - 200 - 161 = about 1,370 calories per day.
- Per hour: 1,370 divided by 24 = about 57 calories.
- Eight hours at that rate: about 457 calories.
- Eight hours at 95% of that rate: about 434 calories.
The same steps for a 40-year-old man at 80 kg and 178 cm give about 1,718 calories per day. That is about 72 calories per hour, or roughly 544 to 573 calories over 8 hours.
There is a second method. The 2024 Adult Compendium of Physical Activities lists sleeping at 1.0 MET. The Compendium defines one MET as 1 kcal per kg per hour. For the 70 kg woman, that gives 70 calories per hour, or 560 over 8 hours. That is about 100 calories above the equation result. The Compendium's own notes on corrected METs explain why: the standard MET can overstate resting metabolism for many people. The equation method uses your age, sex, and height, so it is the better fit here.
The equation explained about 71% of the variation in resting energy between people, so your true figure can differ. To see how sleep fits into a full day, read how to calculate your TDEE.
What changes how many calories you burn asleep?
Body composition does most of the work. A National Institutes of Health study measured 29 adults overnight. Fat-free mass, fat mass, age, sex, and race explained 85% of the difference in sleeping metabolic rate between people.
- Body size. More fat-free mass means a higher rate. Weight is the largest term in the Mifflin-St Jeor equation.
- Age. The equation subtracts 5 calories per day for each year of age.
- Sex. At the same weight, height, and age, the equation gives men 166 more calories per day than women.
- Broken sleep. In the British calorimeter study, the overnight ratio was higher in people with obesity, in late pregnancy, and in people wearing ECG electrodes. The authors put most of that down to disturbed sleep.
- Room temperature. Nine men spent 60 hours in a respiration chamber at 16 degrees C and at 22 degrees C. The cooler room raised energy expenditure, and the response varied between people. The summary gives no figure for the sleep hours alone. See whether you burn more calories in cold or hot weather.
Do you burn more calories in REM or deep sleep?
The differences are real in some studies, but small. In the NIH study, the rate in stage 3 (deep) sleep was 39 calories per day lower than in stage 2. It was 51 calories per day lower than in REM sleep. Those are daily rates, so an hour in one stage instead of another shifts the total by about 2 calories.
A Japanese study of 29 adults in a whole-room calorimeter found a similar order. Energy use was highest during wake periods after sleep onset, and higher in REM than in deep sleep. It also fell during the first half of the night and rose during the second half.
Not every study agrees. A Dutch study of 13 young adults found that energy expenditure did not differ between sleep stages. The only exception was time awake during the night, which cost more. The authors suggested that earlier findings partly reflected the time of night.
The practical point is simple. Chasing more REM or more deep sleep will not change your calorie burn in a way that matters.
Does short sleep change your daily burn and appetite?
Staying awake longer burns slightly more, but people eat more than the difference. In the seven-person study above, 24-hour energy expenditure rose by about 7% during a night of total sleep deprivation. It then fell by about 5% during recovery.
A University of Colorado inpatient study followed 16 adults through 5 days of insufficient sleep. Total daily energy expenditure rose by about 5%. Food intake rose by more, especially after dinner. The participants gained an average of 0.82 kg.
A 2017 meta-analysis pooled 11 intervention studies with 172 participants. After partial sleep deprivation, people ate 385 more calories per day. The analysis found no significant change in total energy expenditure or resting metabolic rate.
The CDC recommends 7 or more hours of sleep per day for adults aged 18 to 60. If you struggle to get there, our sibling site insomnia.md covers sleep problems.
How accurate are wearables for sleep calories?
Treat the overnight number as an estimate. A watch does not measure calories. It works from the profile you enter, plus motion and heart rate.
Published reviews do not report accuracy for calories burned during sleep on its own. They do report on the two inputs. A 2024 umbrella review in Sports Medicine covered 24 systematic reviews. It found wearables mostly underestimated energy expenditure, with a mean bias of minus 3%. Errors in individual studies ranged from minus 21.27% to plus 14.76%.
The same review found that wearables tend to overestimate total sleep time. An earlier systematic review of 22 studies of Fitbit and Jawbone trackers found the same pattern. It also found that the trackers underestimated time awake after sleep onset. Time awake in bed costs more energy than sleep, so a missed wake period is a missed cost.
The equation result above is likely as good a guide as the watch. We cover workout readings in do smartwatches overestimate calories burned.
The bottom line
You burn close to your basal metabolic rate while you sleep, or about 5% less in some studies. Divide a Mifflin-St Jeor result by 24 and multiply by your hours asleep. In the two worked examples here, that gives about 430 to 570 calories over 8 hours. Sleep stage and room temperature move the number only a little. Short sleep is the larger risk for weight, because people eat more than the extra energy they use.
Last updated: October 2026. This article is for informational purposes only and does not constitute medical advice. Equations give estimates, so talk with your doctor or a registered dietitian about your own energy needs and sleep.