Calculate your Basal Metabolic Rate with the Katch-McArdle formula using lean body mass. Ideal for individuals who know their body fat percentage. Includes TDEE estimates.
The Katch-McArdle formula estimates Basal Metabolic Rate (BMR) based on lean body mass rather than total body weight. Developed by Frank Katch and William McArdle, this equation recognizes that metabolically active tissue — primarily skeletal muscle — is the main driver of resting energy expenditure. By factoring in body composition, the Katch-McArdle formula provides a more individualized estimate for people who know their body fat percentage.
Unlike the Harris-Benedict and Mifflin-St Jeor equations, which rely on total weight, height, age, and sex, the Katch-McArdle formula uses a single predictor variable: lean body mass (total weight minus fat mass). This makes it particularly useful for athletes, bodybuilders, and anyone who has had their body composition measured through methods like DEXA, skinfold calipers, or bioelectrical impedance analysis.
This calculator computes your lean body mass from your weight and body fat percentage, applies the Katch-McArdle equation, and provides Total Daily Energy Expenditure (TDEE) estimates across five activity levels to help you plan your nutrition.
The Katch-McArdle formula is the best BMR equation for individuals with atypical body compositions. Standard height-and-weight-based equations can significantly overestimate BMR for people with high body fat and underestimate it for lean, muscular individuals. If you know your body fat percentage — whether from a DEXA scan, skinfold measurement, or body composition scale — the Katch-McArdle formula will give you a more accurate calorie baseline than population-averaged equations.
BMR = 370 + (21.6 × Lean Body Mass in kg) Where: Lean Body Mass (kg) = Total Weight (kg) × (1 − Body Fat % / 100) TDEE = BMR × Activity Factor Sedentary: ×1.2 | Lightly Active: ×1.375 | Moderately Active: ×1.55 | Very Active: ×1.725 | Extra Active: ×1.9
Result: 1,875 kcal/day
For an 85 kg individual with 18% body fat: Lean Body Mass = 85 × (1 − 0.18) = 69.7 kg. BMR = 370 + (21.6 × 69.7) = 370 + 1,505.5 = 1,875.5 ≈ 1,876 kcal/day. At a moderate activity level (×1.55), their TDEE would be approximately 2,907 kcal/day.
Lean body mass (LBM) includes everything in your body except stored fat: skeletal muscle, organs, bones, water, and connective tissue. Skeletal muscle is the largest component and the most metabolically active tissue at rest, burning approximately 13 kcal per kilogram per day. By comparison, fat tissue burns only about 4.5 kcal per kilogram per day. This disparity is why lean mass is such a strong predictor of resting metabolic rate.
Consider using the Katch-McArdle formula when: you have a reliable body fat percentage measurement, your body composition differs significantly from the average population (very lean or very muscular), you are an athlete tracking body composition changes, or you want to compare BMR across different body fat levels to set stage-specific nutrition targets. If you do not have body fat data, the Mifflin-St Jeor equation is the recommended alternative.
Once you have your Katch-McArdle BMR, multiply by your activity factor to get TDEE. For fat loss, subtract 500-750 kcal for about 0.5-0.7 kg per week of loss. For lean muscle gain, add 250-350 kcal. Protein intake during a cut should be 2.0-2.4 g per kg of body weight to preserve lean mass. During a bulk, 1.6-2.2 g per kg is generally sufficient. Reassess your body fat percentage every 4-8 weeks and recalculate as your composition changes.
The primary limitation is its dependency on accurate body fat measurement. A 5% error in body fat estimation translates to roughly 50-80 kcal/day error in BMR. The formula also does not account for metabolic adaptation from prolonged dieting, thyroid conditions, or genetic variation in metabolic efficiency. For clinical precision, indirect calorimetry remains the gold standard.
Katch-McArdle is the only common BMR equation that uses lean body mass as its sole predictor variable. Other equations like Harris-Benedict and Mifflin-St Jeor use total weight, height, age, and sex. Because muscle tissue is the primary driver of resting metabolism, using lean mass directly can provide more accurate results for people whose body composition differs significantly from population averages.
The accuracy of the Katch-McArdle result depends directly on the accuracy of your body fat input. A DEXA scan provides the gold standard measurement (±1-2% error). Skinfold calipers performed by experienced technicians are reasonably accurate (±3-4%). Bioelectrical impedance scales vary widely in accuracy. Even an estimate is better than nothing, but if your body fat input is off by 5 percentage points, your BMR estimate could be off by 50-70 kcal/day.
It depends on your situation. For the general population without body composition data, Mifflin-St Jeor is the most validated equation. For individuals who know their body fat percentage and have atypical body compositions — very lean, very muscular, or very high body fat — Katch-McArdle tends to be more accurate because it accounts for the actual amount of metabolically active tissue.
Age-related metabolic decline is largely driven by age-related muscle loss (sarcopenia). Sex differences in BMR are also largely explained by differences in lean mass. By using lean body mass directly, the Katch-McArdle formula implicitly accounts for both age and sex effects through their impact on muscle mass, making separate variables unnecessary.
The Cunningham equation (500 + 22 × LBM) was developed for athletes and gives slightly higher BMR estimates than Katch-McArdle (370 + 21.6 × LBM). For a person with 70 kg of lean mass, Cunningham predicts about 2,040 kcal/day versus Katch-McArdle's 1,882 kcal/day. The Cunningham equation is preferred for highly trained athletes.
Yes, and it's especially useful during a cut. As you lose fat while preserving muscle, your Katch-McArdle BMR will remain relatively stable, giving you a consistent baseline. Create a 500-750 kcal deficit below your TDEE for a sustainable rate of fat loss (about 0.5-1 lb per week).
Healthy body fat ranges are 10-20% for men and 18-28% for women. Essential fat minimums are approximately 3-5% for men and 10-13% for women. Athletes typically maintain 6-13% (men) or 14-20% (women). Going below essential fat levels is dangerous and unsustainable.
The Katch-McArdle formula can underestimate BMR in obese individuals because excess fat tissue, while less metabolically active than muscle, does contribute to total energy expenditure. For individuals with body fat above 35-40%, the Mifflin-St Jeor equation or adjusted body weight formulas may provide more practical estimates.