The most widely used formula for calculating calories burned during exercise multiplies a value called a MET (metabolic equivalent of task) by your body weight in kilograms and a constant of 0.0175. That gives you calories per minute, which you then multiply by how long you exercised. But calories burned during a workout are only one piece of the picture. Your body burns calories around the clock through several distinct processes, and understanding each one gives you a much more accurate view of your total daily burn.
The MET Formula for Exercise
Every physical activity has been assigned a MET value that reflects its intensity relative to sitting still, which counts as 1 MET. Walking at a moderate pace is roughly 3.5 METs. Running at 6 mph is about 10. Cycling, swimming, weightlifting, even household chores all have published MET values you can look up in the Compendium of Physical Activities.
The formula, developed by exercise physiologists at institutions like the University of Colorado, works like this:
- Calories per minute = 0.0175 × MET value × your weight in kilograms
- Total calories burned = calories per minute × duration in minutes
So if you weigh 70 kg (about 154 pounds) and run for 30 minutes at 6 mph (10 METs), the math is: 0.0175 × 10 × 70 = 12.25 calories per minute, or roughly 368 calories for the full half hour. To convert your weight from pounds to kilograms, divide by 2.2.
This formula is a solid estimate, but it treats everyone of the same weight as identical. It doesn’t account for fitness level, muscle mass, or running form, all of which shift the real number up or down. Still, it’s far more reliable than guessing and more transparent than the number your treadmill spits out.
Your Basal Metabolic Rate: Calories at Rest
Before you burn a single exercise calorie, your body is already using energy to keep your heart beating, your lungs breathing, and your cells functioning. This baseline burn is your basal metabolic rate (BMR), and it typically accounts for 60 to 70 percent of everything you burn in a day.
The Mifflin-St Jeor equation is considered the most accurate formula for estimating BMR without lab equipment:
- Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
- Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
For a 35-year-old woman who weighs 65 kg and stands 165 cm tall, that comes out to (10 × 65) + (6.25 × 165) − (5 × 35) − 161 = 1,370 calories per day just to exist. An older formula called the Harris-Benedict equation is still used in some calculators but tends to overestimate by 5 to 15 percent in people who are overweight.
Your BMR rises with more muscle mass. Muscle tissue burns more calories at rest than fat tissue does, which is why two people at the same weight can have noticeably different resting metabolic rates. This is also why strength training can shift your baseline calorie burn over time.
Total Daily Energy Expenditure
Your total daily energy expenditure (TDEE) combines your BMR with the calories you burn through movement and digestion. The simplest way to estimate it is to multiply your BMR by a physical activity level (PAL) factor. The Food and Agriculture Organization of the United Nations classifies these into three broad categories:
- Sedentary or light activity: multiply BMR by 1.4 to 1.69 (desk job, minimal exercise)
- Active or moderately active: multiply BMR by 1.7 to 1.99 (regular exercise or a physically demanding job)
- Vigorously active: multiply BMR by 2.0 to 2.4 (intense daily training or heavy manual labor)
Using the example above, if that 35-year-old woman exercises moderately most days, her TDEE would be roughly 1,370 × 1.75 = 2,398 calories per day. PAL values above 2.4 are difficult to maintain long term, even for elite athletes. For most people, the realistic range falls between 1.4 and 2.0.
Calories Burned Through Digestion
Your body spends energy breaking down and absorbing the food you eat. This is called the thermic effect of food, and it accounts for roughly 10 percent of your total daily burn. But the number varies dramatically depending on what you’re eating.
Protein has the highest thermic effect, increasing your metabolic rate by 15 to 30 percent of the calories in that protein. Carbohydrates raise it by 5 to 10 percent, and fats by just 0 to 3 percent. This is one reason high-protein diets are often recommended for fat loss: you literally burn more calories digesting protein than you do digesting the same number of calories from fat. If you eat 200 calories of chicken breast, your body may use 40 to 60 of those calories just processing it. Eat 200 calories of butter, and you’ll use fewer than 6.
The Post-Exercise Burn
After you finish a workout, your body doesn’t snap back to its resting state immediately. Oxygen consumption stays elevated while your muscles repair, your body temperature normalizes, and various hormones settle back to baseline. This recovery period burns additional calories beyond what you spent during the exercise itself.
How many extra calories depends almost entirely on intensity. A moderate 80-minute cycling session might produce an additional 130 calories of post-exercise burn. But the real variable is duration of the effect. Low-intensity exercise may keep your metabolism slightly elevated for about 20 minutes. Moderate-intensity work can extend this to around 3 hours. High-intensity intervals or heavy resistance training can keep the burn elevated for over 10 hours, and in some cases, oxygen consumption remains measurably above resting levels 24 hours later.
This effect is real but easy to overestimate. For a typical 30 to 45 minute workout at moderate intensity, the post-exercise bonus adds a modest bump, not a free pass to eat an extra meal.
How Accurate Are Fitness Trackers?
If you rely on a smartwatch to tell you how many calories you burned, the number on your wrist is likely off by a significant margin. Research from Harvard’s School of Engineering found that wearable devices carry estimated error rates of 30 to 80 percent for calorie calculations. That means a watch reporting 400 calories burned could be off by 120 to 320 calories in either direction.
Wearables estimate calories using heart rate data, accelerometer readings, and algorithms trained on population averages. They don’t know your actual muscle mass, fitness level, or movement efficiency. They tend to be more accurate for steady-state cardio like jogging and less accurate for weight training, cycling, or activities where your arms stay relatively still.
The most accurate method available outside a lab is indirect calorimetry, which measures the actual oxygen you consume and carbon dioxide you produce. Every liter of oxygen your body uses burns approximately 5 calories, so measuring gas exchange gives a direct reading of energy expenditure. This is how metabolic testing at sports performance clinics works, but it’s impractical for daily use. For most people, the MET formula paired with a reasonable BMR estimate will give you a more honest picture than your watch.
Why Your Environment Matters Less Than You Think
A common belief is that exercising in cold weather burns significantly more calories because your body works harder to stay warm. The physiology behind this is real: maintaining core body temperature in the cold does require extra energy. However, a large-scale analysis published in iScience found that in practice, adults in modern environments show no meaningful relationship between ambient temperature and total daily energy expenditure. People compensate by wearing warmer clothes, heating their homes, and unconsciously adjusting their behavior. The same held true for hot environments. Unless you’re genuinely shivering for extended periods without adequate clothing, temperature isn’t meaningfully changing your calorie math.
Putting the Numbers Together
To get a practical daily calorie estimate, start with your BMR using the Mifflin-St Jeor equation. Multiply it by the activity factor that honestly reflects your lifestyle. Then, if you want to isolate what a specific workout added, use the MET formula for that activity. Keep in mind that the MET calculation includes your resting calories during that time period, so there’s some overlap with your BMR. For a rough correction, you can subtract 1 MET from the activity’s MET value before plugging it into the formula, which removes the baseline resting burn you would have had anyway.
For example, if running is 10 METs, use 9 METs in the formula to estimate the calories burned above and beyond what you’d have burned sitting on the couch. For a 70 kg person running 30 minutes, that adjusts the number from 368 down to about 331 net additional calories. The difference is small for high-intensity activities but meaningful for lower-intensity ones like walking, where using the full MET value can overstate the benefit by 25 percent or more.