Katch-McArdle BMR Calculator

What is the Katch-McArdle formula?

The Katch-McArdle equation is a predictive formula for basal metabolic rate (BMR) that uses your lean body mass (LBM) instead of total body weight. Because lean tissue (muscle, organs, bone) is more metabolically active than fat, this approach can better reflect the true energy needs of people with higher or lower muscle mass.

Unlike formulas such as Harris–Benedict or Mifflin–St Jeor, Katch–McArdle does not require sex, age, or height in the equation itself. Those variables still matter for health and performance, but the math is driven by how much of your body weight is lean tissue.

How this calculator works

This tool is designed to be flexible and easy to use:

• Metric and imperial units – enter weight in kg or lb, height in cm or in.
• Two ways to enter body composition:
  • Enter body fat % and weight → we compute lean body mass.
  • Or enter lean body mass directly → we back-calculate body fat %.
• Automatic unit conversion for lean body mass and fat mass.
• Activity factor to estimate total daily energy expenditure (TDEE).
• Calorie targets for mild/aggressive weight loss and lean weight gain.

Step-by-step example

Suppose you have:

• Weight = 80 kg
• Body fat = 20%

First compute lean body mass:

Then apply Katch–McArdle:

If you are moderately active (activity factor ≈ 1.55), your estimated TDEE is:

From BMR to daily calorie needs (TDEE)

BMR is the energy your body would use at complete rest. To estimate your total daily energy expenditure (TDEE), we multiply BMR by an activity factor:

• Sedentary (little or no exercise): 1.2
• Lightly active (1–3 days/week): 1.375
• Moderately active (3–5 days/week): 1.55
• Very active (6–7 days/week): 1.725
• Extra active (hard exercise & physical job): 1.9

The calculator then suggests calorie targets:

• Mild weight loss: ~10% below TDEE
• Aggressive weight loss: ~20% below TDEE (short term only)
• Lean weight gain: ~10% above TDEE

These are generic estimates. Individual responses to calorie changes vary based on genetics, hormones, sleep, stress, and training.

Katch-McArdle vs other BMR formulas

Common BMR equations include:

• Mifflin–St Jeor – widely used in clinical nutrition.
• Harris–Benedict – older, still popular in many tools.
• Katch–McArdle – uses lean body mass.

Research comparing these formulas to indirect calorimetry (the lab gold standard) shows that no single equation is perfect for everyone. Katch–McArdle tends to perform well in people whose body composition is known, especially athletes and those with higher muscle mass. However, if your body fat estimate is poor, the advantage disappears and may even become a disadvantage.

When Katch-McArdle is a good choice

• You have a reasonably accurate body fat measurement (DEXA, BIA, calipers).
• You are lean or muscular and standard formulas seem to underestimate your needs.
• You want to track changes in BMR as your body composition changes.

When to be cautious

• Your body fat % is just a rough guess.
• You are using a cheap scale with highly variable readings.
• You have medical conditions that significantly affect metabolism.

In those cases, it can be helpful to compare Katch–McArdle with other formulas and monitor your real-world response (weight trend, performance, hunger, etc.).

Limitations and medical disclaimer

• All BMR equations are statistical estimates, not exact measurements.
• The calculator does not account for pregnancy, illness, medications, or metabolic disorders.
• Calorie targets are for general information only and are not medical or dietary advice.

Always consult a qualified healthcare professional or registered dietitian before making major changes to your diet, exercise, or weight-loss plan.