Mifflin-St Jeor vs Harris-Benedict Equation

Mifflin-St Jeor vs Harris-Benedict: Which BMR Formula Should You Use?

Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to maintain vital functions like breathing, circulation, and body temperature. Both the Mifflin-St Jeor and Harris-Benedict equations estimate BMR from weight, height, and age, but their accuracy differs significantly, and choosing the wrong one can throw your calorie goals off by 100–200 kcal per day.

Harris-Benedict (1919, Revised 1984)

The Harris-Benedict equation was first published in 1919 by James Arthur Harris and Francis Gano Benedict. It was revised by Roza and Shizgal in 1984 using updated coefficients. For decades it was the clinical standard for estimating BMR. The formulas are:

• Men: BMR = 88.362 + 13.397w + 4.799h − 5.677a
• Women: BMR = 447.593 + 9.247w + 3.098h − 4.330a

Where w = weight in kg, h = height in cm, a = age in years.

The problem is that the original 1919 study used a small sample of mostly young, lean men under controlled laboratory conditions. Modern populations are heavier, older on average, and have different body composition profiles — meaning Harris Benedict Male tends to overestimate BMR by 5–15% for contemporary adults.

Mifflin-St Jeor (1990)

The Mifflin St Jeor Male equation was published in 1990 by Mark Mifflin and Sachiko St Jeor using a more representative sample of modern adults. Multiple independent validation studies have confirmed it as the most accurate single-equation BMR estimator for the general adult population.

• Men: BMR = 10w + 6.25h − 5a + 5
• Women: BMR = 10w + 6.25h − 5a − 161

The Calorie calculator uses Mifflin-St Jeor by default for this reason. It is the equation endorsed by the Academy of Nutrition and Dietetics.

Why the Difference Matters

Both equations are just the first step. You multiply BMR by an activity multiplier (sedentary: 1.2 to very active: 1.9) to get Total Daily Energy Expenditure (TDEE). An error in the BMR estimate gets amplified by this multiplier.

Example with a 35-year-old woman, 70 kg, 165 cm: - Harris-Benedict BMR: ~1,474 kcal - Mifflin-St Jeor BMR: ~1,428 kcal - Difference: 46 kcal at rest - With a moderate activity multiplier (1.55): the TDEE difference grows to ~71 kcal/day - Over 30 days: ~2,130 kcal — nearly a pound of potential error in a weight loss plan

For someone trying to lose weight at a 500 kcal/day deficit, using the wrong formula can mean the difference between successfully losing about a pound per week and barely losing any weight at all.

Accuracy in Special Populations

Both equations perform less well in populations far from their study samples:

• Highly obese individuals (BMI > 35): Both underperform; some research suggests the Mifflin-St Jeor with actual body weight is still the best standard option available
• Athletes with high muscle mass: Both equations underestimate BMR since muscle tissue burns more calories than the formulas assume
• Elderly adults: Muscle loss with age means both can overestimate; the Mifflin-St Jeor is still preferred

For athletes or highly muscular individuals, using lean body mass-based equations (like Katch-McArdle) provides better accuracy when body fat percentage is known.

When to Use Harris-Benedict

Harris-Benedict remains embedded in older clinical software, dietary analysis tools, and historical research papers. If you're comparing outcomes to studies published before 2000, or working with legacy clinical nutrition software, Harris-Benedict ensures consistency with the existing data. Otherwise, there is no compelling reason to use it over Mifflin-St Jeor.