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KATCH-MCARDLE BMR CALCULATOR

Calculate your Basal Metabolic Rate using the Katch-McArdle formula, which uses lean body mass for the most accurate calorie estimate. See your TDEE across all activity levels.

CALCULATE YOUR BMR

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WHAT IS THE KATCH-MCARDLE FORMULA?

The Katch-McArdle formula estimates your Basal Metabolic Rate (BMR) based on lean body mass rather than total body weight. The formula is: BMR = 370 + (21.6 x lean body mass in kg). Because it uses lean mass, it provides a more accurate estimate for individuals who know their body composition.

Developed by Frank Katch and William McArdle, this formula recognizes that metabolic rate is primarily driven by metabolically active tissue (muscle, organs) rather than total body weight including fat stores. This makes it particularly valuable for athletes, bodybuilders, and anyone tracking body composition.

HOW IT DIFFERS FROM MIFFLIN-ST JEOR

The Mifflin-St Jeor equation uses total weight, height, age, and gender to estimate BMR. It assumes an average body composition and works well for the general population but can be inaccurate for people who are significantly more muscular or carry more body fat than average.

Katch-McArdle bypasses these assumptions entirely by using lean mass directly. If you have an accurate body fat measurement, Katch-McArdle will give you a more personalized BMR estimate. If you do not know your body fat percentage, Mifflin-St Jeor is a reasonable alternative.

WHY LEAN MASS MATTERS FOR BMR

Muscle tissue is far more metabolically expensive than fat tissue. Each pound of muscle burns roughly 6-7 calories per day at rest, while fat tissue burns only about 2 calories per pound. This difference means that body composition has a significant impact on daily calorie needs.

Two people who weigh the same but have different body fat percentages will have meaningfully different metabolic rates. The leaner individual burns more calories at rest, requires more food to maintain weight, and has a higher TDEE at every activity level.

CHOOSING YOUR ACTIVITY LEVEL

Activity multipliers convert your BMR into Total Daily Energy Expenditure (TDEE). Be honest about your typical week rather than your best week. Most people overestimate their activity level, which leads to eating too much when trying to lose weight.

If you train 3-4 times per week with moderate intensity and have a desk job, "Lightly Active" or "Moderately Active" is likely appropriate. Reserve "Very Active" and "Extra Active" for those who train hard almost daily or have physically demanding jobs in addition to their training.

USING KATCH-MCARDLE FOR CUTTING AND BULKING

For a cut, subtract 300-500 calories from your TDEE. This creates a moderate deficit that promotes fat loss while preserving lean mass. Aggressive deficits (more than 750 calories below TDEE) increase the risk of muscle loss and metabolic adaptation.

For a bulk, add 200-400 calories above your TDEE. This provides enough surplus to support muscle growth without excessive fat gain. As your body composition changes over time, recalculate periodically since your BMR will shift as lean mass increases or decreases.

FREQUENTLY ASKED QUESTIONS

What is the Katch-McArdle formula?
The Katch-McArdle formula calculates Basal Metabolic Rate (BMR) using lean body mass: BMR = 370 + (21.6 x lean mass in kg). Unlike other BMR formulas that use total weight, age, and gender, Katch-McArdle focuses solely on lean mass, making it more accurate for people who know their body fat percentage.
How is Katch-McArdle different from Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor and Harris-Benedict use total body weight, height, age, and gender to estimate BMR. They assume an average body composition and can overestimate BMR for people with high body fat or underestimate it for very muscular individuals. Katch-McArdle uses lean body mass directly, providing more accurate results when body fat percentage is known.
Do I need to know my body fat percentage?
Yes. The Katch-McArdle formula requires body fat percentage to calculate lean body mass. You can estimate body fat using calipers, DEXA scans, bioelectrical impedance scales, or visual comparison charts. For the most accurate BMR calculation, use a reliable body fat measurement method like DEXA or hydrostatic weighing.
What activity level should I choose?
Choose the level that best matches your typical week. Sedentary means desk work with no exercise. Lightly active is 1-3 light workouts per week. Moderately active is 3-5 sessions of moderate intensity. Very active is 6-7 hard training sessions. Extra active is for athletes training multiple times daily or those with physically demanding jobs on top of exercise.
Can I use this for cutting or bulking?
Absolutely. Once you know your TDEE (BMR x activity multiplier), subtract 300-500 calories for a moderate cut, or add 200-400 calories for a lean bulk. The Katch-McArdle formula is especially useful during dieting phases because it accounts for lean mass, giving you a more accurate baseline as your body composition changes.
Why does lean mass matter for BMR?
Muscle tissue is metabolically active and burns significantly more calories at rest than fat tissue. Two people at the same weight but different body compositions will have very different BMRs. A 180 lb person at 12% body fat burns more calories at rest than a 180 lb person at 30% body fat because they carry substantially more lean tissue.
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