BMR from the tissue that matters
Mifflin-St Jeor and Harris-Benedict infer body composition from sex, age, height and weight. Katch-McArdle skips the inference and uses the answer directly: lean body mass, the metabolically active tissue that drives most of your resting burn.
Formula: BMR = 370 + 21.6 × LBM (kg), where LBM = weight × (1 − body fat % / 100). One formula for everyone — sex and age drop out because lean mass already encodes them.
Worked example
An 80 kg man at 15% body fat carries 68 kg of lean mass: 370 + 21.6 × 68 = 1,839 kcal/day. The same man computed by Mifflin-St Jeor at age 30 and 180 cm comes out at 1,780 — Katch-McArdle credits his above-average muscularity.
Flip the case to 30% body fat at the same weight and Katch-McArdle returns 1,580 kcal, where Mifflin would still say 1,780 — a 200 kcal overestimate that could quietly stall a diet.
The catch: garbage in, garbage out
The formula is only as good as your body-fat number. DEXA scans are the gold standard; tape-measure methods like the US Navy formula are ±3–4%; consumer bioimpedance scales can swing several points with hydration alone.
Practical rule: use Katch-McArdle when you're notably muscular or lean and have a credible body-fat estimate. Otherwise Mifflin-St Jeor's simplicity wins.
Put it into practice: run your own numbers with the related calculator — free, instant, and nothing leaves your browser.
Frequently asked questions
Is Katch-McArdle more accurate than Mifflin-St Jeor?
Only when your body-fat estimate is good. With an accurate figure it shines for athletic and very lean physiques; with a guessed figure it can be worse than the equations it replaces.
How do I find my body fat percentage?
DEXA or BodPod for accuracy, the Navy tape method for a free reasonable estimate (our body-fat calculator implements it), and bioimpedance scales for trends rather than absolutes.
Why doesn't the formula ask my sex or age?
Because lean body mass already captures what sex and age proxy for in other equations — it's the more direct measurement of the same underlying driver.
More guides
- What Is TDEE?
- What Is BMR?
- Mifflin-St Jeor Calculator
- Harris-Benedict Calculator
- BMR vs TDEE: What's the Difference?
- What Are MET Values?
- What Is NEAT?
- The Thermic Effect of Food
- Activity Multipliers Explained
- What Is a Calorie?
- Metabolic Adaptation Explained
- The Calorie Deficit, Explained
- 500-Calorie Deficit
- 1,000-Calorie Deficit
- 300-Calorie Deficit
- How Many Calories to Lose 1 Pound a Week
- How Many Calories to Lose 2 Pounds a Week
- Reverse Dieting
- Maintenance Phase
- Calorie Cycling
- How Accurate Are TDEE Calculators?
- Not Losing Weight in a Calorie Deficit? 7 Real Reasons
- Is 1,200 Calories a Day Safe?
- Should You Eat Back Exercise Calories?
- How Long Does Metabolic Adaptation Last?
- Do You Burn Fewer Calories as You Lose Weight?
- Why Your Maintenance Calories Keep Changing
- Calorie Cycling vs Flat Deficit
- How to Avoid Muscle Loss on GLP-1 Medications
Sources
- McArdle WD, Katch FI, Katch VL. Exercise Physiology: Nutrition, Energy, and Human Performance. Wolters Kluwer.
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center. 1984. [link]