Katch-McArdle Calculator

Calculate BMR and TDEE based on lean body mass using the Katch-McArdle formula

About the Katch-McArdle Calculator

The Katch-McArdle Calculator is a specialized tool designed to estimate Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE). Unlike traditional metabolic equations that rely on age, height, and total weight, this formula focuses exclusively on lean body mass. This approach makes it a favorite among athletes, bodybuilders, and fitness enthusiasts who have a body composition that differs significantly from the average person. By ignoring fat mass—which is metabolically less active than muscle—the Katch-McArdle formula provides a more precise caloric baseline for those who know their body fat percentage.

Fitness professionals and nutritionists use this tool to create highly customized meal plans. Because muscle tissue requires more energy to maintain than adipose tissue, individuals with high muscle density often find that standard formulas underestimate their caloric needs. This calculator bridges that gap, providing a calculation that rewards muscle mass and ignores the weight of body fat. Whether you are aiming for a precise "cutting" phase or a clean "bulking" cycle, understanding your LBM-based metabolic rate is essential for achieving specific body composition goals.

Formula

BMR = 370 + (21.6 * LBM in kg)

The Katch-McArdle formula calculates Basal Metabolic Rate (BMR) using Lean Body Mass (LBM). LBM represents your total body weight minus your fat mass. To find LBM in kilograms, take your weight in kilograms and multiply it by (1 - body fat percentage).

The number 370 is a constant, while 21.6 is the multiplier applied to every kilogram of lean tissue. Once the BMR is established, Total Daily Energy Expenditure (TDEE) is calculated by multiplying the BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (extra active).

Worked examples

Example 1: A 90kg male athlete with 15% body fat and a moderate activity level.

1. Calculate Lean Body Mass: 90kg * (1 - 0.15) = 76.5 kg LBM.
2. Calculate BMR: 370 + (21.6 * 76.5) = 2,022.4 calories.
3. Calculate TDEE: 2,022.4 * 1.55 (Moderate Activity) = 3,134.7 calories.

Result: 2,324 calories per day. This represents the total energy needed to maintain current weight with moderate exercise.

Example 2: A 65kg female powerlifter with 18% body fat seeking her BMR.

1. Calculate Lean Body Mass: 65kg * (1 - 0.18) = 53.3 kg LBM.
2. Calculate BMR: 370 + (21.6 * 55.5) = 1,569 calories (rounded).

Result: 1,570 calories BMR. This is the baseline energy needed before adding any activity.

Common use cases

Athletes with high muscle mass who find standard formulas underestimate their energy needs.
Individuals undergoing a body recomposition phase where fat loss and muscle gain occur simultaneously.
People who have recently had a DXA scan and want to use their precise lean mass data for diet planning.
Bodybuilders calculating a precise caloric surplus for a lean bulk.

Pitfalls and limitations

Inaccurate body fat measurements will lead to an incorrect BMR calculation.
The formula does not account for the thermic effect of food (TEF), which can vary based on protein intake.
Overestimating your activity level (TDEE multiplier) is the most common cause of weight loss plateaus.
It may be less accurate for very elderly individuals where organ metabolic rate changes independant of muscle mass.

Frequently asked questions

is katch mcardle more accurate than mifflin st jeor

The Katch-McArdle formula is generally more accurate for individuals with low body fat or high muscle mass because it bases energy needs on Lean Body Mass. Most other calculators, like Mifflin-St Jeor, use total body weight, which can overestimate needs for the obese or underestimate them for athletes.

how do i find my lean body mass for katch mcardle

To use this formula, you must first calculate your body fat percentage, either through skinfold calipers, DXA scans, or bioelectrical impedance. Once you have your body fat percentage, subtract that weight from your total body weight to find your Lean Body Mass in kilograms.

does katch mcardle work for both men and women

No, unlike the Harris-Benedict or Mifflin-St Jeor equations, the Katch-McArdle formula does not include a variable for sex. This is because it assumes that a pound of muscle burns the same amount of energy regardless of whether it belongs to a man or a woman.

should i use katch mcardle if i am a bodybuilder

If you have an athletic build or a significant amount of muscle, this formula is highly recommended. However, if you do not know your body fat percentage or have a high body fat percentage, the results may be less reliable than standard weight-based formulas.

difference between BMR and TDEE in katch mcardle calculation

BMR is the energy your body burns at total rest just to keep organs functioning, while TDEE is your BMR multiplied by an activity factor to account for exercise, work, and movement during the day.