You can estimate your daily calorie burn using a simple formula based on your age, weight, height, and sex, then adjusting for how active you are. The result won’t be perfect, but it gets most people within a reasonable range. For a precise number, you’d need a clinical metabolic test, though few people actually need that level of accuracy.
Where Your Calories Actually Go
Before estimating your burn, it helps to understand what’s using all that energy. Your body burns calories in three main ways, and exercise is the smallest piece.
Your basal metabolic rate, the energy your body uses just to keep you alive (breathing, circulating blood, maintaining body temperature, repairing cells), accounts for 60% to 70% of everything you burn in a day. This is the calorie cost of simply existing, even if you stayed in bed for 24 hours. Another 10% goes toward digesting food. The remaining 20% to 30% fuels all your physical movement, from formal exercise to fidgeting in your chair.
That breakdown surprises most people. It means the single biggest factor in your daily burn isn’t your workout. It’s your body size, age, and composition.
The Mifflin-St Jeor Formula
The most reliable way to estimate your resting calorie burn at home is the Mifflin-St Jeor equation. A systematic review in the Journal of the American Dietetic Association found it predicted resting metabolic rate within 10% of the actual measured value in more people (both normal weight and obese) than any other formula, with the narrowest error range.
Here’s how it works:
- For men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
- For women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
To convert your weight, divide pounds by 2.2. To convert height, multiply inches by 2.54. The number you get is your resting metabolic rate in calories per day.
To estimate your total daily burn, multiply that number by an activity factor: 1.2 if you’re mostly sedentary, 1.375 for light exercise a few days a week, 1.55 for moderate exercise three to five days a week, 1.725 for hard daily exercise, and 1.9 for very intense training or a physically demanding job. For example, a 35-year-old woman who weighs 150 pounds, stands 5’5″, and exercises moderately would have a resting rate of about 1,370 calories and a total daily burn around 2,120.
How MET Values Work for Specific Activities
If you want to know how many calories a particular workout burns, MET values are the standard tool. MET stands for metabolic equivalent of task. One MET equals the energy you use sitting quietly. An activity rated at 5 METs burns five times that amount.
The formula is straightforward: calories burned = METs × weight in kg × hours. A 70 kg (154 lb) person running at 6 mph (a 10-minute mile pace, rated at 9.8 METs) for 30 minutes would burn roughly 343 calories.
Some common MET values to give you a sense of scale:
- Walking at a brisk pace (3.5 mph): 4.3 METs
- Running at 5 mph (12-min mile): 8.3 METs
- Running at 7 mph (8.5-min mile): 11.0 METs
- Swimming laps, moderate effort: 5.8 METs
- Swimming laps, vigorous effort: 9.8 METs
- Weight training, typical session: 3.5 METs
- Weight training, vigorous effort: 6.0 METs
Notice that weight training sits surprisingly low on the scale. A standard lifting session burns fewer calories per minute than a moderate swim. That said, the calorie benefit of strength training extends beyond the session itself, because muscle tissue raises your resting metabolic rate over time.
Why Muscle Mass Changes Your Baseline
A pound of muscle burns roughly 4.5 to 7 calories per day at rest. A pound of fat burns far less, about 50 to 100 times less than the equivalent weight of muscle. That gap is real, but it’s smaller than many fitness influencers claim. Adding 10 pounds of muscle might raise your resting burn by 45 to 70 calories a day, not the hundreds some sources suggest.
The organs in your body (brain, liver, heart, kidneys) actually drive a much larger share of resting calorie burn. Their metabolic rate per unit of weight is 15 to 40 times greater than muscle. You can’t grow a bigger liver through training, but this explains why body composition alone doesn’t fully predict someone’s metabolic rate.
The Hidden Variable: Non-Exercise Movement
One of the biggest wildcards in your daily calorie burn has nothing to do with the gym. Non-exercise activity thermogenesis, or NEAT, covers every movement that isn’t structured exercise: pacing while on the phone, taking the stairs, cooking, carrying groceries, tapping your foot. According to research by Mayo Clinic scientist James Levine, NEAT can vary by up to 2,000 calories per day between two people of similar size.
That’s an enormous range, and it’s the main reason two people with the same weight, age, and workout schedule can have wildly different calorie needs. A person with a desk job who drives everywhere and relaxes on the couch in the evening sits at the low end. Someone who walks to work, stands most of the day, and stays on their feet in the evening sits at the high end. No formula fully captures this, which is one reason all estimates are approximations.
How Accurate Are Fitness Trackers?
Wearable devices like Apple Watch, Fitbit, and Garmin estimate your calorie burn using heart rate data, movement sensors, and algorithms that factor in your profile information. They’re convenient, but their accuracy leaves a lot to be desired.
A Stanford University study tested seven popular wearables against gold-standard lab measurements. Calorie estimates ranged from 27% to 93% error. The most accurate device in the study, the Fitbit Surge, still overestimated by 27%. The worst performer nearly doubled the actual calorie burn. Heart rate tracking was far more reliable across all devices, but the leap from heart rate to calorie estimation introduces significant guesswork.
This doesn’t mean trackers are useless. They’re good for tracking relative trends: if your watch says you burned more this week than last week, that’s probably true directionally. But treating the specific calorie number as gospel, especially if you’re eating back “earned” calories after a workout, can easily lead you astray by hundreds of calories per day.
Clinical Metabolic Testing
The most accurate way to measure your calorie burn is indirect calorimetry, considered the gold standard. You breathe into a mask or mouthpiece connected to a machine that measures the oxygen you consume and the carbon dioxide you exhale. From that gas exchange, it calculates your resting energy expenditure precisely.
This test is commonly used in hospital settings for critically ill patients, but it’s also available at some sports medicine clinics, university research labs, and nutrition practices for the general public. A session typically costs $100 to $250 and takes 15 to 30 minutes. You’ll usually need to fast beforehand and avoid exercise that morning. The result gives you a measured resting metabolic rate rather than an estimated one, which you can then multiply by an activity factor for your total daily burn.
For most people managing their weight, the Mifflin-St Jeor formula combined with honest self-assessment of activity level gets close enough. Clinical testing is worth considering if you’ve been following a calorie target based on a formula and your weight isn’t responding the way you’d expect, or if you have a medical condition that might affect your metabolism.
Putting It All Together
Start with the Mifflin-St Jeor equation to get your resting number, then multiply by the activity factor that honestly matches your lifestyle. Use MET values when you want to estimate the burn from a specific workout. Treat your fitness tracker as a trend indicator, not a precise calorie counter. And remember that the biggest portion of your daily burn, around two-thirds, happens automatically just to keep your body running. The rest is split between digesting food and all the ways you move throughout the day, with non-exercise movement often outweighing your actual workouts.
No method short of a lab test will give you an exact number. But combining a validated formula with realistic activity assessment gets most people within 10% to 15% of their true calorie burn, which is precise enough to make informed decisions about eating and exercise.