Your body burns between 1,300 and 2,000 calories a day just keeping you alive, before any intentional exercise. This baseline burn, called your basal metabolic rate (BMR), accounts for 60% to 70% of all the energy you use in a day. The rest comes from digesting food, everyday movements, and maintaining your body temperature. Understanding these numbers helps you make sense of your actual energy needs.
What Your Body Spends Energy on at Rest
Even if you stayed in bed all day and didn’t move, your body would still burn a significant number of calories. Your heart beats roughly 100,000 times a day. Your lungs expand and contract. Your cells divide, your kidneys filter blood, and your brain processes information nonstop, including during sleep. All of this requires fuel.
The biggest energy consumers are your brain, liver, and skeletal muscle. Your brain alone uses about 24% of your resting energy, despite making up only about 2% of your body weight. Your liver handles another 20%, processing nutrients and filtering toxins. Skeletal muscle accounts for around 18%, even when you’re not using it. Body fat, by contrast, is relatively inactive, contributing only about 8% of your resting calorie burn.
This is why body composition matters so much. A pound of muscle burns roughly 6 calories per day at rest, while a pound of fat burns only 2. That gap adds up across your entire body. Someone with more lean mass will naturally burn more calories doing absolutely nothing than someone of the same weight with a higher body fat percentage.
Typical Calorie Burn by Sex and Body Size
Research pooling hundreds of studies found that the average adult burns about 0.86 calories per kilogram of body weight per hour at rest. Men run slightly higher at 0.89 calories per kilogram per hour, while women average 0.84. For a 70 kg (154-pound) man, that works out to roughly 1,495 calories per day from resting metabolism alone. For a 60 kg (132-pound) woman, it’s closer to 1,210.
Young adults with normal body weight have the highest resting metabolic rates per kilogram. Young, normal-weight men burn about 1.0 calorie per kilogram per hour, while young, normal-weight women burn around 0.92. As body weight increases, the per-kilogram rate drops, though total calorie burn still goes up because there’s simply more tissue to maintain. A 250-pound person burns more total resting calories than a 150-pound person, even though each pound of their body is slightly less metabolically active on average.
The Other Ways Your Body Burns Calories
Your resting metabolism is the largest piece, but two other processes make up the remainder of your daily burn without any gym time.
Digesting food costs energy. Your body has to break down, absorb, and store everything you eat, and some nutrients take more work than others. Protein is the most expensive to process: your body uses 20% to 30% of the calories in protein just to digest it. Carbohydrates cost 5% to 10%, and fat costs almost nothing at 0% to 3%. So a 200-calorie chicken breast might only net you around 150 usable calories, while 200 calories of butter delivers nearly all 200. This “thermic effect of food” typically adds up to about 10% of your total daily calorie intake.
Non-exercise movement covers everything from fidgeting and standing to walking around your house and typing. This category, sometimes called NEAT, varies wildly between people. Simply standing increases your energy burn 10% to 20% above resting levels. Walking doubles or even triples it. Research has found that lean individuals tend to move more throughout the day in small, unconscious ways. If a sedentary person adopted those habits (more standing, more walking between tasks, more general restlessness) they could burn an additional 280 to 350 calories per day without ever setting foot in a gym.
How Age Changes Your Baseline Burn
Your resting metabolism drops by roughly 10% each decade after age 20. By the time you reach 50, you’re burning about 30% fewer calories at rest than you did in your early twenties. For someone whose BMR was 1,600 calories at age 20, that’s a drop to roughly 1,120 by middle age.
The primary driver is muscle loss. Adults lose muscle mass gradually as they age, and since muscle burns three times more calories per pound than fat, each pound of muscle lost lowers your daily burn. Hormonal shifts and reduced physical activity accelerate this cycle. Strength training is the most direct way to slow the decline, because maintaining muscle mass keeps your resting metabolism higher than it would otherwise be.
Cold Exposure and Extra Calorie Burn
Your body also burns calories to maintain its core temperature of about 98.6°F. In comfortable room temperatures, this cost is baked into your BMR. But when you’re exposed to cold, the burn increases. A large evidence review from the UK Health Security Agency found that mildly cool air temperatures (around 60°F to 68°F) increased daily energy expenditure by 50 to 200 calories. More extreme cold pushed the number much higher: some studies using cold-water cooling suits found increases of over 1,000 calories per day, and the most extreme lab conditions (near-freezing temperatures in minimal clothing) added an estimated 2,600 extra calories.
For everyday life, the practical takeaway is modest. Keeping your home a few degrees cooler or spending more time outdoors in cool weather might add 50 to 200 calories of burn. Shivering increases it further, but most people avoid shivering for good reason.
Estimating Your Own Resting Burn
The two most commonly used formulas for estimating resting metabolism are the Mifflin-St Jeor and Harris-Benedict equations. Both use your height, weight, age, and sex to produce an estimate. Neither is perfect. Compared to lab measurements, both formulas carry a margin of error around 9% to 11%, meaning a true resting burn of 1,500 calories might be estimated anywhere from 1,335 to 1,665.
To get a rough number for yourself using Mifflin-St Jeor:
- Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age) – 161
This gives you resting calories only. To estimate your total daily burn without structured exercise, multiply that number by 1.2 to account for digestion and everyday movement. A 35-year-old woman who is 5’5″ and weighs 140 pounds would get a resting estimate of about 1,345 calories, and a total daily estimate around 1,614. A 35-year-old man who is 5’10” and weighs 180 pounds would land at roughly 1,765 resting calories and 2,118 total.
These formulas work best for adults of average body composition. They tend to overestimate for people with high body fat and underestimate for people with above-average muscle mass, precisely because of the difference in how much energy muscle and fat tissue require.