Katch-McArdle Calculator
Calculate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) using the precise Katch-McArdle formula. Unlike standard calculators, this tool prioritizes Lean Body Mass (LBM) for higher accuracy, especially for athletes or individuals with varying body compositions.
Calculator Interface
Katch-McArdle Formula
The Katch-McArdle formula is widely considered the most accurate equation for calculating Basal Metabolic Rate (BMR) for individuals who know their body composition. Unlike the Mifflin-St Jeor or Harris-Benedict equations, which rely on total body weight, Katch-McArdle ignores fat mass entirely and calculates energy needs based solely on Lean Body Mass (LBM).
This distinction is crucial because muscle tissue is significantly more metabolically active than fat tissue. Two people weighing 100kg can have vastly different caloric needs if one is an athlete (10% body fat) and the other is sedentary (35% body fat). The formula is:
BMR = 370 + (21.6 × Lean Body Mass in kg)
By focusing on LBM, this calculator prevents underestimating calories for muscular individuals and overestimating calories for those with higher body fat percentages.
Katch-McArdle Formula Activity Level
Once BMR is calculated, your Total Daily Energy Expenditure (TDEE) calculator output is derived by multiplying BMR by an activity factor. Selecting the correct multiplier is vital for accurate results.
| Level | Factor | Description |
|---|---|---|
| Sedentary | 1.2 | Desk job, little to no exercise. |
| Lightly Active | 1.375 | Light exercise/sports 1-3 days/week. |
| Moderately Active | 1.55 | Moderate exercise/sports 3-5 days/week. |
| Very Active | 1.725 | Hard exercise/sports 6-7 days/week. |
| Extra Active | 1.9 | Very hard exercise/physical job or 2x training. |
Most individuals overestimate their activity. If you exercise 1 hour a day but sit for the remaining 15 hours (office work), a “Sedentary” or “Lightly Active” multiplier often yields a better starting point for weight loss than “Moderate”.
Katch-McArdle vs Mifflin
The comparison of Katch-McArdle vs Mifflin-St Jeor is common. The Mifflin-St Jeor equation is the current industry standard for the general population because it only requires weight, height, age, and sex—variables everyone knows.
- Use Mifflin-St Jeor if you do not know your body fat percentage. It provides a reliable average but can err by ±10% for outliers.
- Use Katch-McArdle if you have a reliable body fat measurement (DEXA scan, calipers, or hydrostatic weighing). It is the “gold standard” for athletes and bodybuilders.
If you use the Mifflin formula while having a very high muscle mass, it may slightly underestimate your needs. Conversely, Katch-McArdle scales linearly with your muscle gain.
Katch-McArdle Formula Women
The Katch-McArdle formula for women is mathematically identical to the version for men: $370 + (21.6 \times LBM)$. The formula does not “see” gender; it only sees metabolic tissue.
However, estimating Lean Body Mass without a body fat measurement differs by sex. If you use our “Estimate LBM” mode (Mode C), we utilize the Boer Formula:
- Women: LBM = $(0.252 \times Weight) + (0.473 \times Height) – 48.3$
- Men: LBM = $(0.407 \times Weight) + (0.267 \times Height) – 19.2$
Women naturally carry more essential body fat than men. Therefore, even at the same weight and height, a woman will typically have a lower LBM and consequently a lower BMR than a man. Using the Katch-McArdle calculator accounts for this biological difference automatically.
Frequently Asked Questions
How accurate is the Katch-McArdle calculator?
It is widely considered the most accurate formula for those with known body composition. However, the final accuracy depends entirely on the accuracy of your body fat input.
Can I use this if I don’t know my body fat percentage?
Yes, select “Estimate based on Height/Weight” in the dropdown above. We will use the Boer formula to estimate your lean mass, though measuring your body fat will always be superior.
Does age matter in Katch-McArdle?
Technically, no. The formula assumes that the metabolic slowdown associated with aging is primarily due to muscle loss. If you maintain your LBM as you age, your BMR remains largely stable according to this equation.
