When calculating your daily energy expenditure or structuring a fat-loss diet, everything begins with your Basal Metabolic Rate (BMR). BMR is the baseline caloric cost of keeping your heart beating, lungs ventilating, kidneys filtering, and brain functioning over a 24-hour period at rest.
However, when you use a metabolic calculator online, you are often prompted to choose between different scientific equations: Mifflin-St Jeor, Revised Harris-Benedict, or Katch-McArdle. But which equation is scientifically proven to be the most accurate for your body type? You can test each formula directly using our BMR Calculator.
1. Mifflin-St Jeor: The Clinical Standard for General Populations
Developed in 1990 by Dr. MD Mifflin and Dr. ST St Jeor, this formula was created to replace the outdated 1919 Harris-Benedict equation. It calculates BMR using total body weight, height, age, and biological sex.
The Formula:
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age (years) + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) - 5 × age (years) - 161
Clinical Verdict: In 2005, the Academy of Nutrition and Dietetics conducted a systematic review comparing all predictive metabolic equations against indirect calorimetry (the lab gold standard using oxygen exchange). The researchers concluded that Mifflin-St Jeor predicted resting metabolic rate within ±10% for over 82% of individuals, making it the premier equation for non-athletic and generally active populations.
2. Katch-McArdle: The Gold Standard for Lean Lifters and Athletes
Unlike Mifflin-St Jeor, the Katch-McArdle formula does not care about your height, age, or gender. Instead, it relies on a single crucial variable: Lean Body Mass (LBM).
The Formula:
BMR = 370 + (21.6 × Lean Body Mass in kg)
Why is this superior for muscular individuals? Adipose tissue (body fat) is metabolically sluggish, burning only about 4.5 kcal per kilogram per day. Skeletal muscle tissue, by contrast, is highly active, burning ~13 kcal per kilogram per day at complete rest. Because Mifflin-St Jeor assumes standard population body fat percentages, it under-predicts BMR for heavily muscled bodybuilders and over-predicts for individuals carrying high body fat.
To use Katch-McArdle, measure your body composition first using our Body Fat Calculator and Lean Body Mass Calculator.
3. Revised Harris-Benedict: The Historical Standard
Originally derived in 1919 and updated by Roza & Shizgal in 1984, the Revised Harris-Benedict equation is still widely taught in older clinical textbooks. While reliable, modern research demonstrates that Harris-Benedict tends to overestimate resting energy needs by 5% to 15% in modern populations, which can lead people to set their dieting calorie targets slightly too high.
Comparative Decision Summary
- Choose Mifflin-St Jeor if: You do not know your exact body fat percentage and have average muscle mass.
- Choose Katch-McArdle if: You are a trained athlete, weightlifter, or bodybuilder who knows your body fat percentage within 2-3%.
- Choose Revised Harris-Benedict if: You are comparing outputs against historical medical records.
Once you have isolated your baseline BMR, scale it into a complete daily target using our TDEE Calculator.