Katch-McArdle Calculator

The Katch-McArdle equation estimates your Basal Metabolic Rate (BMR) from your lean body mass rather than from total weight, height, and age. Because muscle is the main driver of resting metabolism, this approach is often the most accurate choice for lean, muscular, or very heavy individuals — provided you know your body-fat percentage.

The Formula

First derive lean body mass from weight and body fat, then plug it into the Katch-McArdle BMR equation and scale to TDEE.

Worked Example

A 75 kg person at 18% body fat, moderately active (×1.55):

• LBM = 75 × (1 − 0.18) = 61.5 kg
• BMR = 370 + 21.6 × 61.5 = 370 + 1328.4 = 1,698 kcal
• TDEE = 1,698 × 1.55 ≈ 2,632 kcal/day

Activity Multipliers

When Katch-McArdle Wins

Equations like Harris-Benedict and Mifflin-St Jeor estimate metabolism from size alone, so they can misjudge people whose body composition is unusual — a 90 kg bodybuilder and a 90 kg sedentary person get the same number despite very different metabolisms. Because Katch-McArdle uses lean mass, it separates those two cases cleanly.

The Catch: Body-Fat Accuracy

The equation is only as reliable as your body-fat input. A 5% error in body fat shifts LBM by several kilograms and BMR by 80-100 kcal. Use a consistent, validated method — DEXA, calipers, or a good BIA scale — and re-measure under similar conditions.

Note: This is an energy-needs estimate for planning, not medical advice. Verify against real-world results by tracking weight over a few weeks and adjusting calories accordingly.