Most people burn roughly 40 to 80 calories per hour while sleeping, which adds up to about 300 to 600 calories over a full eight-hour night. The exact number depends on your body weight, muscle mass, age, and even the temperature of your bedroom. That’s a wide range, so understanding what drives it can help you figure out where you personally fall.
How Your Body Burns Calories During Sleep
Sleep looks passive, but your body is doing a lot of behind-the-scenes work. Your brain is consolidating memories, your cells are repairing tissue, your liver is processing nutrients, and your heart and lungs keep running on autopilot. All of that requires energy.
Your sleeping metabolic rate is closely tied to your basal metabolic rate (BMR), which is the energy your body needs just to keep its basic systems running. During sleep, your metabolic rate drops about 5 to 17% below your waking resting level. Body temperature dips by roughly 0.4°C as part of the natural sleep cycle, and your muscles relax, both of which reduce energy demand. A simple way to estimate your hourly sleep calorie burn: take your BMR (which you can calculate with an online tool using your age, sex, height, and weight), divide by 24, and then reduce that number by about 15%.
Why Sleep Stages Matter
Not all hours of sleep burn calories at the same rate. Your brain cycles through lighter sleep, deep sleep, and REM (rapid eye movement) sleep multiple times per night, and each stage has a different metabolic cost. Research using whole-body calorimetry found that REM sleep burns noticeably more energy than the other stages. In one study, energy expenditure during REM sleep measured about 25.7 calories per kilogram of fat-free mass per day, compared to roughly 25.2 during lighter sleep and 24.8 during deep sleep.
The difference exists because REM sleep is when your brain is most active, processing emotions and dreams. Brain tissue is energy-hungry, so periods of intense neural activity push calorie burn higher. You spend more time in REM during the second half of the night, which means the last few hours of a full night’s sleep are slightly more metabolically active than the first few. Cutting sleep short doesn’t just leave you tired; it also trims the portion of your night where calorie burn is highest.
Body Weight and Muscle Mass
Your body size is the single biggest factor in how many calories you burn overnight. A person who weighs 130 pounds will burn closer to 40 calories per hour during sleep, while someone at 200 pounds might burn 60 to 70 or more. Larger bodies simply require more energy to maintain basic functions like circulation and breathing.
Composition matters just as much as total weight, though. Muscle tissue is more metabolically active than fat tissue, so two people at the same weight can have meaningfully different sleep calorie burns depending on how much of their body is lean muscle versus fat. People who strength train or are generally more physically active tend to carry more muscle, which keeps their resting metabolic rate (and therefore their sleeping metabolic rate) higher. This is one reason why regular exercise influences calorie burn around the clock, not just during workouts.
Room Temperature Makes a Real Difference
Sleeping in a cooler room forces your body to work harder to maintain its core temperature, and that extra work burns extra calories. Research comparing energy expenditure at different ambient temperatures found significant differences. At 18°C (about 64°F), resting energy expenditure was roughly 96 calories per day higher than at 28°C (82°F). Even a moderate cool-down to 22°C (72°F) increased daily burn by about 73 calories compared to 28°C.
Part of this effect comes from brown fat, a specialized type of fat tissue that generates heat by burning calories. Cooler temperatures activate brown fat more aggressively. You don’t need to shiver all night to see a benefit. Simply keeping your bedroom in the mid-60s Fahrenheit range is enough to nudge calorie expenditure upward, and it happens to align with the temperature range most sleep experts recommend for the best sleep quality anyway.
How Eating Before Bed Affects the Number
If you eat a meal shortly before falling asleep, your body will still be digesting that food as you drift off, which temporarily raises your metabolic rate. This is called the thermic effect of food: your body spends energy breaking down, absorbing, and storing nutrients. However, the bump is smaller than you might hope. Research shows that the thermic effect of food is actually lower during sleep than during wakefulness, meaning your body processes that late meal less “expensively” than it would if you stayed awake. A lighter evening meal produces a smaller thermic effect than a heavier one, and falling asleep after eating blunts the effect further.
This doesn’t mean eating before bed is necessarily bad for you, but it does mean you shouldn’t count on a bedtime snack to meaningfully boost your overnight calorie burn.
Sleep Disorders and Metabolic Rate
Poor sleep doesn’t just affect how you feel the next day. It can also change the metabolic equation in counterintuitive ways. People with obstructive sleep apnea, for instance, actually show an elevated resting metabolic rate compared to people without the condition. Their bodies are working harder during sleep because of repeated airway obstructions and the stress response that follows each one.
But that higher calorie burn doesn’t translate to weight loss. In fact, the opposite tends to happen. Sleep apnea disrupts the hormones that regulate hunger and fullness, specifically leptin and ghrelin. Studies consistently find abnormally high levels of both hormones in people with sleep apnea, which creates a state of leptin resistance. The result is that the body’s increased energy expenditure triggers an even larger increase in appetite, leading to overeating that more than offsets the extra calories burned. This helps explain the well-documented link between sleep apnea and weight gain.
Insomnia and chronic sleep deprivation create similar hormonal disruptions. Even in people without a diagnosed sleep disorder, consistently getting fewer than six hours of sleep per night is associated with changes in hunger hormones that promote weight gain over time.
A Quick Estimate for Your Body
To get a rough personal number, you can use this simplified approach:
- Step 1: Calculate your BMR using the Harris-Benedict equation or any online BMR calculator (you’ll need your age, sex, height, and weight).
- Step 2: Divide that daily BMR by 24 to get your hourly resting burn.
- Step 3: Multiply by 0.85 to account for the metabolic slowdown during sleep.
- Step 4: Multiply that hourly figure by the number of hours you sleep.
For a 155-pound, 30-year-old woman, this typically works out to around 50 calories per hour, or about 400 calories over eight hours. A 185-pound man of the same age would burn closer to 60 calories per hour, totaling roughly 480 over a full night. These are estimates, not precise measurements, but they get you in the right ballpark. Fitness trackers that incorporate heart rate data can offer a somewhat more personalized number, though they still carry a margin of error.