Basal metabolic rate is the energy your body needs at complete rest just to keep organs, breathing and circulation running — it excludes digestion and movement, which is why total daily burn (TDEE) is always higher.

Which formula is more accurate?

Mifflin-St Jeor (1990), the default here, is validated as the most accurate general-population equation in comparison studies. Harris-Benedict (1919, revised 1984) is older and tends to run slightly higher for the same inputs.

Why does BMR matter if I want my daily calorie target?

BMR is the starting point: multiply it by an activity factor to get TDEE, then adjust up or down from TDEE for weight goals. Use the TDEE calculator for that next step.

Does this account for muscle mass?

No — both formulas use only sex, age, height and weight. Two people of the same size but very different muscle mass will have different true BMRs; a body-fat-based formula like Katch-McArdle would be needed to capture that, which this tool does not include.

BMR Calculator

Estimate your basal metabolic rate — the calories your body burns at rest — with the Mifflin-St Jeor or Harris-Benedict formula, toggled in one tool.

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Formula: Mifflin-St Jeor: BMR = 10·kg + 6.25·cm − 5·age + 5 (men) / − 161 (women)

Worked examples

25-year-old man, 180 cm, 75 kg
A typical adult male result using the default Mifflin-St Jeor equation.
35-year-old woman, 160 cm, 65 kg
Shows how the −161 female offset in Mifflin-St Jeor lowers the estimate relative to a same-size man.
Same man as example 1, Harris-Benedict formula
The older Harris-Benedict equation for the same person, typically 60–100 kcal higher than Mifflin-St Jeor.

What BMR means

Basal metabolic rate is the number of calories your body burns just to stay alive at complete rest — keeping your heart beating, lungs breathing, brain running and cells repairing, with no digestion and no movement included. It's the floor under your daily energy use, not the total: your actual Total Daily Energy Expenditure (TDEE) adds digestion, daily activity and exercise on top of it.

How the calculator works

It estimates BMR from your sex, age, height and weight using the Mifflin-St Jeor equation (the default) or the older Harris-Benedict equation, toggled in one tool rather than split across separate pages.
It also shows BMR expressed per hour, which is a useful sanity check — most adults burn somewhere between 55 and 90 kcal an hour at rest, and a wildly different number usually means an input was mistyped.

Why the two formulas differ

Harris-Benedict was published in 1919 and revised in 1984. Mifflin-St Jeor followed in 1990, built from a larger and more representative sample, and in comparison studies against measured resting metabolic rate it predicts more accurately for more people than any other widely used general-population equation — which is why it's the default here. For most adults, Harris-Benedict runs 60–100 kcal higher for identical inputs. Neither formula accounts for muscle mass directly: two people with the same height, weight, age and sex but very different body composition will have different true BMRs, which a body-fat-based formula like Katch-McArdle would capture and this one does not.

How to use the result

BMR by itself isn't a calorie target — it's an input to one. To find out how many calories you actually burn in a day, multiply this BMR by an activity factor (sedentary through very active), which is exactly what the TDEE calculator does automatically. From there, eating below your TDEE creates a deficit for weight loss and eating above it creates a surplus for weight gain; BMR tells you the number you should never eat consistently below without medical supervision, since going under it for extended periods risks slowing metabolism and losing muscle rather than just fat.

Limits

This is a population-average estimate, not a measurement of your individual metabolism. Real BMR varies by roughly ±10–15% around any formula's prediction due to genetics, muscle mass, thyroid function, and other factors the equation can't see. Pregnancy, certain medications, and medical conditions that affect metabolism will also move your true value away from what the formula predicts. If you want a more precise number, indirect calorimetry (a clinical metabolic test) is the gold standard — this calculator is a free, fast starting estimate, not a substitute for that or for medical advice.

Frequently asked questions

What is BMR?: Basal metabolic rate is the energy your body needs at complete rest just to keep organs, breathing and circulation running — it excludes digestion and movement, which is why total daily burn (TDEE) is always higher.
Which formula is more accurate?: Mifflin-St Jeor (1990), the default here, is validated as the most accurate general-population equation in comparison studies. Harris-Benedict (1919, revised 1984) is older and tends to run slightly higher for the same inputs.
Why does BMR matter if I want my daily calorie target?: BMR is the starting point: multiply it by an activity factor to get TDEE, then adjust up or down from TDEE for weight goals. Use the TDEE calculator for that next step.
Does this account for muscle mass?: No — both formulas use only sex, age, height and weight. Two people of the same size but very different muscle mass will have different true BMRs; a body-fat-based formula like Katch-McArdle would be needed to capture that, which this tool does not include.

These calculators give general estimates from published formulas. They are not medical advice and do not account for your individual health; talk to a qualified professional before changing your diet or training.