Basal Metabolic Rate — Katch-McArdle Calculator
Estimate basal metabolic rate from lean body mass with the Katch-McArdle equation, plus daily energy expenditure at your activity level.
How it works
Lean body mass = weight × (1 − body fat%/100) · BMR = 370 + 21.6 × LBM (kg) · TDEE = BMR × activity factor
The Katch-McArdle equation predicts basal metabolic rate from lean body mass alone, on the reasoning that muscle and organs — not fat — drive most resting energy use. That makes it more accurate than weight-and-height formulas for lean or muscular people, provided you have a reasonable body-fat estimate. Multiplying the BMR by an activity factor yields total daily energy expenditure, the anchor for any calorie plan; because it depends on body-fat accuracy, treat the number as a starting point and refine it against real-world results.
Worked example
For a 75 kg person at 20% body fat: lean mass = 75 × (1 − 0.20) = 60 kg, so BMR = 370 + 21.6 × 60 = 370 + 1,296 = 1,666 kcal/day. At a moderate 1.55 activity factor, TDEE ≈ 1,666 × 1.55 = 2,582 kcal/day.
Sources: Katch-McArdle formula
Frequently asked questions
When is Katch-McArdle better than Mifflin-St Jeor?
It tends to be more accurate for lean or muscular people because it is driven by lean body mass rather than total weight. Its weakness is that it needs a body-fat percentage, which is itself an estimate.
How do I find my body-fat percentage?
Methods range from skinfold callipers and bioelectrical scales to DEXA scans. Even a rough figure improves the estimate, but the more accurate the body-fat number, the better the BMR.
What is the difference between BMR and TDEE?
BMR is the energy your body uses at complete rest. TDEE multiplies it by an activity factor to include movement, exercise and digestion, so it is always higher and is the number you plan calories around.
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Educational estimate using standard published formulas — not medical advice, a diagnosis, or a substitute for clinical judgement. Dosing, diagnosis and treatment must be decided by a qualified clinician using validated tools and the full clinical picture.