Katch-McArdle Calculator
Calculate your BMR with the Katch-McArdle equation from lean body mass, plus TDEE by activity. Best when you know your body-fat percentage.
By Jonas Lindemann · Updated · How we build our calculators
2628kcal/day
maintenance calories (TDEE)
1696
BMR (kcal/day)
61.4 kg
lean body mass
Note: Katch-McArdle bases BMR on lean mass, so accuracy depends on a good body-fat estimate. It is a planning guide, not medical advice.
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Calculation Method
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.
BMR = 370 + 21.6 × LBM(kg)
TDEE = BMR × activityFactor
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
| Activity level | Factor |
|---|---|
| Sedentary | 1.20 |
| Light (1-3 days/week) | 1.375 |
| Moderate (3-5 days/week) | 1.55 |
| Active (6-7 days/week) | 1.725 |
| Very active | 1.90 |
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.
Frequently Asked Questions
It estimates BMR as 370 + 21.6 x lean body mass in kg. Because muscle drives resting metabolism, basing the estimate on lean mass can be more accurate than size-based formulas.
It shines for lean, muscular, or very heavy people whose body composition is unusual. A 90 kg bodybuilder and a 90 kg sedentary person get different, more realistic numbers.
Lean body mass is derived from total weight and body-fat percentage. A 5% error in body fat shifts BMR by 80-100 kcal, so use a consistent, validated body-fat method.
If you have a reliable body-fat figure, Katch-McArdle is often the better choice. If you do not, Harris-Benedict or Mifflin-St Jeor, which use only size and age, are more practical.