Katch-McArdle vs Mifflin-St Jeor: Which BMR Formula Should You Use?

Blog › Health · 6 min read · Published 2026-05-04

How the Katch-McArdle equation compares to Mifflin-St Jeor, when each is most accurate, and how to use them for athletes versus general population.

Why Two Formulas Exist

Resting metabolic rate (RMR) — the calories your body burns at rest — drives every nutrition target you set. Two formulas dominate: Mifflin-St Jeor uses age, height, weight, and sex; Katch-McArdle uses lean body mass. Each shines in a different population.

Mifflin-St Jeor: The General Population Standard

Published in 1990, the Mifflin-St Jeor equation is widely considered the most accurate predictive formula for the general adult population. It does not require body-fat measurement, which makes it accessible.

Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

Studies show Mifflin-St Jeor predicts measured RMR within ~10% for most adults — better than the older Harris-Benedict equation.

Katch-McArdle: The Athlete's Choice

Katch-McArdle bypasses age and sex by using lean body mass directly. Because muscle is the primary metabolically active tissue at rest, this approach is more accurate for lean and athletic populations where body weight alone misrepresents metabolic activity.

Formula: RMR = 370 + 21.6 × LBM(kg)

Katch-McArdle outperforms Mifflin-St Jeor when body fat is below ~15% (men) or ~22% (women) — populations where total weight overstates fat mass relative to muscle.

Which Should You Use?

Use Mifflin-St Jeor if you don't know your body fat with reasonable accuracy, are sedentary or moderately active, or have an average body composition.

Use Katch-McArdle if you have a recent DEXA, hydrostatic, or quality caliper measurement; you train seriously; you carry visibly more muscle than average; or your physique-based goals require precision.

Translating BMR to Daily Calories

Multiply BMR by an activity factor: 1.2 sedentary, 1.375 light, 1.55 moderate, 1.725 very active, 1.9 extreme. The result is total daily energy expenditure (TDEE) — your maintenance calorie target.

From there, subtract 10–25% for cuts, add 5–15% for lean bulks, or eat at TDEE for maintenance.

Common Pitfalls

Using the wrong activity multiplier — most people overestimate activity. Choose one level lower than you think.
Using Katch-McArdle with bathroom-scale body fat readings — those are often off by 5–8%, defeating the formula's accuracy gain.
Updating your BMR only once a year — recalculate after every 5 kg change in body weight.

The Katch-McArdle RMR Calculator handles the math instantly and includes activity multipliers so you can compare your athletic-tuned BMR against standard predictions.