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BMR Calculator (BMR / TDEE)

Enter sex, age, height, weight (optional body fat) and activity level to get BMR and TDEE, with a table comparing all three formulas.

Basal metabolic rate is the energy burned at complete rest, and total daily expenditure is BMR times an activity factor — anyone cutting or bulking needs both numbers first. Enter sex, age, height, weight, optionally body-fat percentage, and activity level, and the table gives BMR and TDEE for all three formulas: Mifflin-St Jeor, Harris-Benedict and Katch-McArdle.

On the differences between them: Mifflin-St Jeor is the currently accepted general-purpose formula; Harris-Benedict is the classic older one and reads about 5% high for modern populations; Katch-McArdle needs a body-fat percentage and is the better choice for a heavily muscled person. With all three side by side, take the middle value or pick the one that fits your situation.

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How to use

  1. Enter sex, age, height, weight and activity level.
  2. Add body-fat percentage if you want the Katch-McArdle row.
  3. Compare BMR and TDEE across the three formulas.
  4. Take the middle value, or the formula that suits your build.

How it works

What the three BMR formulas are

Mifflin-St Jeor: men's BMR = 10 x weight + 6.25 x height - 5 x age + 5, with +5 replaced by -161 for women. For a 70 kg, 175 cm, 30-year-old man, BMR = 700 + 1,093.75 - 150 + 5 = 1,648.75 kcal. The revised Harris-Benedict uses another set of coefficients (men 88.362 + 13.397W + 4.799H - 5.677A), giving 1,695.667 kcal for the same person.

TDEE and activity factors

Katch-McArdle ignores height and age, using only lean body mass: BMR = 370 + 21.6 x lean mass (kg), where lean mass = weight x (1 - body-fat%). In the example with 20% body fat, lean mass is 56 kg, so BMR = 370 + 1,209.6 = 1,579.6 kcal. It suits those whose muscle mass markedly departs from average, but requires knowing body-fat percentage.

Why the three formulas differ

TDEE = BMR x activity factor. The five levels are sedentary 1.2, light 1.375, moderate 1.55, high 1.725 and very high 1.9. The three formulas usually differ by 5-10%, within estimation error, so don't agonize over "which is exactly right" — pick one and calibrate by actual weight change.

Calculation basis: BMR is estimated with three published formulas — Mifflin-St Jeor, revised Harris-Benedict (1984) and Katch-McArdle — with activity factors from 1.2 to 1.9. Results are estimates: individual variation can reach ±10%, and they do not replace advice from a doctor or registered dietitian.

Code example

JavaScript Three BMR formulas 

function bmrAll({ male, age, hCm, wKg, bodyFatPct }) {
  const s = male ? 5 : -161;
  const msj = 10 * wKg + 6.25 * hCm - 5 * age + s;          // Mifflin
  const hb = male
    ? 88.362 + 13.397 * wKg + 4.799 * hCm - 5.677 * age
    : 447.593 + 9.247 * wKg + 3.098 * hCm - 4.330 * age;    // Harris
  const lbm = wKg * (1 - (bodyFatPct || 25) / 100);
  const katch = 370 + 21.6 * lbm;                           // Katch
  return { msj, hb, katch };
}

Python The same three formulas in Python 

def bmr_all(male, age, h_cm, w_kg, body_fat=25):
    s = 5 if male else -161
    msj = 10 * w_kg + 6.25 * h_cm - 5 * age + s
    hb = (88.362 + 13.397 * w_kg + 4.799 * h_cm - 5.677 * age
          if male else
          447.593 + 9.247 * w_kg + 3.098 * h_cm - 4.330 * age)
    lbm = w_kg * (1 - body_fat / 100)
    return {"msj": msj, "hb": hb, "katch": 370 + 21.6 * lbm}

# TDEE = BMR × activity factor (1.2 sedentary to 1.9 very active)

FAQ

What's the difference between BMR and total daily expenditure?

BMR is the minimum expenditure maintaining vital functions (lying still); TDEE = BMR x activity factor, including walking, work and exercise. How much to eat should follow TDEE; using BMR would be clearly too low.

Which of the three BMR formulas should I choose?

Ordinary people default to Mifflin-St Jeor, closest to modern populations; the revised Harris-Benedict runs a few percent higher at normal weight with simple data; if you train and know your body-fat percentage (especially with high muscle mass), Katch-McArdle is more accurate. The three usually differ within 10%.

Why must Katch-McArdle have the body-fat percentage?

Its only input is lean body mass, with no height or age. Without body-fat percentage you can't derive the muscle-to-fat ratio, and the result is distorted, so this tool warns to fill it in rather than arbitrarily returning a number.

Why is my BMR different from others'?

BMR is jointly determined by weight, height, age and sex, so different people should differ under the same formula. What truly warrants caution is "eating by the formula but not changing" — usually the activity factor is set too high, or the food log missed cooking oil and drinks.

Does BMR decline with age?

Yes. In the formula, each added year costs men 5 kcal and women likewise 5 kcal; more importantly, muscle mass declines yearly after 30, and without strength training the actual drop is often larger than the formula.

For fat loss, can I eat below my BMR?

Not advisable long-term. Below BMR easily triggers metabolic adaptation, muscle loss and rebound. The steady approach is TDEE minus 300-500 kcal while ensuring protein intake; if TDEE minus 500 is still below BMR, your activity is too low — first increase daily movement.

How does this differ from the site's calorie calculator?

The calorie calculator focuses on "how much to eat daily" (with fat-loss / maintenance / muscle-gain target calories), while this tool focuses on "how BMR is computed" — comparing three formulas side by side and explaining whom each suits. Both use the same activity factors, so their numbers agree.

Are my weight and body-fat percentage saved?

They never leave your device. Computation runs in the browser with no upload endpoint; if you use history, records are written only to local localStorage, clearable in one click, and gone on close in incognito mode.