What is the Katch-McArdle formula?

BMR = 370 + (21.6 × lean body mass in kilograms). It was introduced by Frank Katch and William McArdle and is widely regarded as the most accurate BMR formula for athletic populations because it uses lean mass instead of total body weight.

How is this different from the Harris-Benedict or Mifflin-St Jeor formula?

Harris-Benedict and Mifflin-St Jeor use total weight, height, age, and sex. Katch-McArdle uses only lean body mass, so sex and age are not needed. This makes it more accurate for muscular or lean individuals and less biased by gender assumptions.

What is lean body mass?

Lean body mass (LBM) is total body weight minus fat mass. It includes muscles, bones, organs, and water. LBM (kg) = body weight (kg) × (1 − body fat % ÷ 100).

How do I find my lean body mass?

The most accurate methods are DEXA scan, hydrostatic weighing, or a validated bioelectrical impedance device. If you know your total weight and body fat percentage you can use the derive tab on this calculator to compute LBM automatically.

What activity multiplier should I choose?

Sedentary (desk job, no planned exercise) = 1.2. Lightly active (1–3 days/week) = 1.375. Moderately active (3–5 days/week) = 1.55. Very active (6–7 days hard training) = 1.725. Extra active (physical job plus hard daily training) = 1.9. When in doubt, choose the level below what you think — people typically overestimate activity.

Is BMR the same as TDEE?

No. BMR is the energy your body uses at complete rest just to sustain vital functions. TDEE (Total Daily Energy Expenditure) multiplies BMR by your activity factor to estimate actual daily calorie burn including movement and exercise.

How many calories below TDEE should I eat to lose fat?

A deficit of 300–500 kcal/day produces roughly 0.3–0.5 kg of fat loss per week while preserving muscle. Deficits over 1,000 kcal/day increase the risk of muscle loss. Consult a registered dietitian for personalized guidance.

Katch-McArdle BMR Calculator

Enter your lean body mass directly — or derive it from weight and body fat — to get your precise BMR and TDEE using the Katch-McArdle formula.

Input Mode

Lean Body Mass (kg)

From DEXA, InBody, or a body composition test.

Activity Level

Enter your lean body mass and click Calculate to see your results.

BMR

—

kcal / day at rest

TDEE

—

kcal / day (active)

Inputs Used

Lean Body Mass

—

Activity Multiplier

—

Calorie Targets

Aggressive cut (−1000 kcal) —

Moderate cut (−500 kcal) —

Maintenance (TDEE) —

Lean bulk (+250 kcal) —

Aggressive bulk (+500 kcal) —

TDEE Across All Activity Levels

Sedentary (×1.2) —

Lightly active (×1.375) —

Moderately active (×1.55) —

Very active (×1.725) —

Extra active (×1.9) —

Formula: BMR = 370 + (21.6 × LBM_kg) • TDEE = BMR × activity multiplier

Summary

The Katch-McArdle BMR Calculator uses the formula BMR = 370 + (21.6 × lean body mass in kg) to estimate your resting calorie needs from lean mass alone — no age or sex required. Because it ignores fat tissue, it is more accurate than Harris-Benedict or Mifflin-St Jeor for athletes and lean individuals. Enter your LBM directly or derive it from weight and body fat percentage, then select your activity level to see your TDEE and five calorie targets.

How it works

Enter your lean body mass (LBM) directly if you know it, or switch to the derive tab and enter total weight plus body fat percentage.
The calculator computes LBM = weight × (1 − body fat / 100).
The Katch-McArdle formula is applied: BMR = 370 + (21.6 × LBM in kg).
Choose your activity level from the five standard multipliers.
Your BMR, TDEE, and five calorie targets (aggressive cut to aggressive bulk) are displayed instantly.

Use cases

Athletes who know their lean body mass from a DEXA scan or InBody device.
Personal trainers setting precise calorie targets for clients with known body composition.
People comparing Katch-McArdle BMR against Harris-Benedict or Mifflin-St Jeor estimates.
Bodybuilders planning a cut or bulk phase who track lean mass changes over time.
Anyone who wants a formula that rewards muscle mass instead of penalizing it.
Nutritionists verifying calorie prescriptions against a lean-mass-based baseline.

Frequently Asked Questions

Last updated: 2026-05-28 · Reviewed by Nham Vu