Your body burns calories in three ways: maintaining basic functions at rest, digesting food, and physical activity. The largest share, roughly 60 to 70 percent of your daily calorie burn, comes from just keeping your body alive. To calculate your total daily calories burned, you start by estimating that resting rate, then layer on the energy cost of movement and digestion.
What Makes Up Your Daily Calorie Burn
Your total daily energy expenditure (TDEE) has three components. The biggest is your basal metabolic rate (BMR), the calories your body uses for breathing, circulating blood, regulating temperature, and keeping organs running while you do absolutely nothing. This accounts for 60 to 70 percent of everything you burn in a day.
The second component is the thermic effect of food, which is the energy your body spends digesting and absorbing what you eat. This adds roughly 10 percent to your daily total. Not all foods cost the same to digest: protein increases your metabolic rate by 15 to 30 percent of the calories consumed, carbohydrates by 5 to 10 percent, and fats by just 0 to 3 percent. This is one reason high-protein diets feel metabolically “expensive.”
The third and most variable component is physical activity, from fidgeting at your desk to running a marathon. For sedentary people this might be 20 percent of the total. For very active people it can rival BMR.
Step 1: Estimate Your Resting Metabolic Rate
The most widely recommended formula is the Mifflin-St Jeor equation. It uses your weight in kilograms, height in centimeters, and age in years:
- Men: (10 × weight) + (6.25 × height) – (5 × age) + 5
- Women: (10 × weight) + (6.25 × height) – (5 × age) – 161
So a 35-year-old woman who weighs 70 kg (154 lbs) and stands 165 cm (5’5″) would calculate: (10 × 70) + (6.25 × 165) – (5 × 35) – 161 = 700 + 1,031 – 175 – 161 = 1,395 calories per day at rest. A man with the same stats would get 1,561 (the only difference is adding 5 instead of subtracting 161).
If you know your body fat percentage, you can use a formula that accounts for muscle mass directly. The Katch-McArdle equation works like this: first calculate your lean body mass by subtracting your fat mass from your total weight (total weight minus total weight times body fat percentage). Then plug it in: BMR = 370 + (21.6 × lean body mass in kg). This is especially useful if you carry significantly more or less muscle than average, since muscle tissue burns more calories at rest than fat.
Step 2: Factor In Your Activity Level
Once you have your BMR, multiply it by a physical activity level (PAL) factor that reflects your typical day. These multipliers come from research measuring actual energy expenditure in free-living people:
- Bed rest or completely sedentary: 1.2
- Seated work, little to no exercise: 1.4 to 1.5
- Seated work with some walking and standing: 1.6 to 1.7
- Standing or walking most of the day: 1.8 to 1.9
- Heavy physical work or very active lifestyle: 2.0 to 2.4
Using the example above, that 35-year-old woman with a BMR of 1,395 who has an office job but exercises a few times a week might use a multiplier of 1.6. Her estimated TDEE: 1,395 × 1.6 = 2,232 calories per day. If she were mostly sedentary with no structured exercise, it would drop to about 1,953 (1,395 × 1.4).
Be honest with yourself when choosing a multiplier. Most people with desk jobs and a few weekly workouts fall in the 1.4 to 1.6 range. The 2.0+ range is reserved for people doing hours of physical labor or serious athletic training daily.
Step 3: Estimate Calories From Specific Exercises
If you want to calculate the burn from a particular workout rather than using a blanket activity multiplier, you can use MET values. A MET (metabolic equivalent of task) represents how many times harder an activity is compared to sitting quietly. Sitting has a MET of 1. Walking at a moderate pace (about 3 mph) has a MET of roughly 3.5. Running at 6 mph is around 10. Cycling at a moderate effort is about 8.
The formula is: calories burned = MET × weight in kg × duration in hours. A 70 kg person walking briskly for 45 minutes: 3.5 × 70 × 0.75 = about 184 calories. The same person running for 30 minutes at 6 mph: 10 × 70 × 0.5 = 350 calories.
You can look up MET values for hundreds of activities in the Compendium of Physical Activities, a database maintained by researchers at Arizona State University. Everything from gardening (3 to 5 METs) to competitive swimming (8 to 11 METs) has a published value.
How Accurate Are These Numbers
Every formula gives you an estimate, not a measurement. The Mifflin-St Jeor equation is considered the most accurate of the common prediction formulas, but it can still be off by 10 percent or more for any given person. Your genetics, hormone levels, gut microbiome, and the exact composition of your body all introduce variability that no simple equation captures.
Fitness trackers and smartwatches add another layer of uncertainty. Research from Harvard’s School of Engineering found that wearable devices can have error rates of 30 to 80 percent when estimating calories burned. Heart rate monitoring helps, but the algorithms these devices use still rely on population averages that may not match your physiology. Treat the number on your wrist as a rough guide, not a precise measurement.
The most reliable approach is to use a formula as your starting point, then track your actual weight and food intake over two to four weeks. If your weight stays stable, your calorie estimates are close to reality. If you’re gaining or losing, adjust your estimate by 200 to 300 calories and re-evaluate.
Age, Muscle, and Metabolism Myths
A common belief is that metabolism drops sharply in your 30s or 40s, making weight gain inevitable. A large-scale study published in Science and covered by Harvard Health found something different: basal metabolic rate stays remarkably stable between ages 20 and 60 when you account for changes in body composition. The real issue is that people tend to lose muscle and gain fat gradually over those decades, and muscle burns more calories at rest than fat does. The metabolic “slowdown” most people experience is largely a body composition problem, not an aging problem.
After age 60, metabolism does decline, at roughly 0.7 percent per year. But for anyone between 20 and 60, maintaining or building muscle through resistance training is the most effective way to keep your resting metabolic rate from drifting downward.
Putting It All Together
Here’s the simplest path to a useful number. Convert your weight to kilograms (divide pounds by 2.2) and your height to centimeters (multiply inches by 2.54). Plug those into the Mifflin-St Jeor equation to get your BMR. Multiply by the activity factor that honestly reflects your daily life. The result is your estimated total daily calorie burn.
For a quick sanity check: most adult women burn between 1,600 and 2,400 calories per day, and most adult men burn between 2,000 and 3,000. If your calculation lands wildly outside those ranges, double-check your unit conversions. If you want to go further, use MET values to calculate specific workouts on top of a sedentary baseline, or invest in a formula that uses lean body mass if you know your body fat percentage. No method is perfect, but combining a solid formula with real-world tracking over a few weeks gets you close enough to make meaningful decisions about your diet and exercise.