What is the difference between the original and revised Harris-Benedict equations?

The original Harris-Benedict equations were published in 1919 based on indirect calorimetry of 136 men, 103 women, and 94 children. The 1984 revision by Roza and Shizgal recalculated the coefficients using updated data and statistical methods, resulting in different intercept and slope constants for both male and female formulas.

Why does BMR decline with age in the formula?

The negative age coefficient reflects the population-level trend of declining lean body mass and reduced cellular metabolic activity with advancing age. The equation incorporates a fixed age penalty of approximately 5.7 kcal/day per year for males and 4.3 kcal/day per year for females, derived from cross-sectional regression analysis.

How does this differ from the Mifflin-St Jeor equation?

The Mifflin-St Jeor equation was published in 1990 using a larger, more contemporary sample. It typically produces estimates 5–10% lower than Harris-Benedict for the same inputs. Both are population-derived linear models; neither directly measures individual metabolic rate.

Can this estimate be used for total daily energy expenditure?

No. BMR represents resting metabolism only. Total daily energy expenditure requires multiplying BMR by an activity factor (often 1.2 to 2.0) to account for physical activity, the thermic effect of food, and non-exercise activity thermogenesis. This calculator returns only the basal component.

What measurement conditions does the equation assume?

The Harris-Benedict equations assume standard indirect calorimetry conditions: post-absorptive state (8–12 hours fasted), supine rest, thermoneutral environment, and absence of acute illness or psychological stress. Real-world measurements taken under different conditions may deviate from the estimate.

Body Composition

BMR Calculator (Harris-Benedict)

Estimate basal metabolic rate using the 1984 revised Harris-Benedict equation.

Last updated: 22 April 2026

What this tool does

This calculator estimates basal metabolic rate (BMR) using the 1984 revised Harris-Benedict equation published by Roza and Shizgal. It requires weight, height, age, and biological sex as inputs, then applies sex-specific formulas to estimate daily resting energy expenditure in kilocalories. The equation was derived from studies of healthy adults and provides a population-average estimate of the calories the body burns at complete rest to maintain vital functions.

Inputs

Result

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Formula Used

BMR = {13.397 w + 4.799 h - 5.677 a + 88.362 9.247 w + 3.098 h - 4.330 a + 447.593 male female

w

Weight in kg

h

Height in cm

a

Age in years

s

Sex (male/female)

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This calculator applies the revised Harris-Benedict equations published in 1984 to estimate basal metabolic rate—the number of calories the body expends at complete rest to maintain vital functions such as respiration, circulation, and cellular metabolism.

How BMR Calculator (Harris-Benedict) works

The tool accepts weight in kilograms, height in centimeters, age in years, and biological sex. It then applies sex-specific linear regression equations derived from indirect calorimetry studies. For males, the formula is 88.362 + (13.397 × weight_kg) + (4.799 × height_cm) − (5.677 × age). For females, it is 447.593 + (9.247 × weight_kg) + (3.098 × height_cm) − (4.330 × age). The output is an estimate of daily energy expenditure at rest, expressed in kilocalories per day.

The formula

Male: BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age in years)
Female: BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age in years)

These coefficients were established through a 1984 revision of the original 1919 Harris-Benedict standards, incorporating updated indirect calorimetry data from larger, more diverse samples.

Where this method is most accurate

The revised Harris-Benedict equations were derived primarily from healthy adults of European descent measured under controlled laboratory conditions. Accuracy tends to be highest for individuals with body compositions near population norms. The equations do not account for variations in lean mass percentage, metabolic adaptation, thyroid function, or genetic polymorphisms affecting metabolic rate. Measurement error in weight or height inputs propagates directly into the estimate.

What this tool does not do

This calculator does not provide total daily energy expenditure; it estimates resting metabolism only. It does not account for physical activity, thermogenesis from food digestion, or non-exercise activity thermogenesis. It does not generate meal plans, macronutrient targets, or training recommendations. The output is a population-derived estimate, not an individualized assessment of metabolic health or a substitute for indirect calorimetry or doubly labeled water measurement.

Disclaimer

This tool is provided for educational and informational purposes only. It is not medical, nutritional, or training advice. The calculator implements a published equation; individual metabolic rates vary. Consult qualified professionals before making decisions related to nutrition, exercise programming, or health management.

Questions

What is the difference between the original and revised Harris-Benedict equations?: The original Harris-Benedict equations were published in 1919 based on indirect calorimetry of 136 men, 103 women, and 94 children. The 1984 revision by Roza and Shizgal recalculated the coefficients using updated data and statistical methods, resulting in different intercept and slope constants for both male and female formulas.
Why does BMR decline with age in the formula?: The negative age coefficient reflects the population-level trend of declining lean body mass and reduced cellular metabolic activity with advancing age. The equation incorporates a fixed age penalty of approximately 5.7 kcal/day per year for males and 4.3 kcal/day per year for females, derived from cross-sectional regression analysis.
How does this differ from the Mifflin-St Jeor equation?: The Mifflin-St Jeor equation was published in 1990 using a larger, more contemporary sample. It typically produces estimates 5–10% lower than Harris-Benedict for the same inputs. Both are population-derived linear models; neither directly measures individual metabolic rate.
Can this estimate be used for total daily energy expenditure?: No. BMR represents resting metabolism only. Total daily energy expenditure requires multiplying BMR by an activity factor (often 1.2 to 2.0) to account for physical activity, the thermic effect of food, and non-exercise activity thermogenesis. This calculator returns only the basal component.
What measurement conditions does the equation assume?: The Harris-Benedict equations assume standard indirect calorimetry conditions: post-absorptive state (8–12 hours fasted), supine rest, thermoneutral environment, and absence of acute illness or psychological stress. Real-world measurements taken under different conditions may deviate from the estimate.

Sources & Methodology

Applies the 1984 revised Harris-Benedict equations (Roza & Shizgal, Am J Clin Nutr 1984). Males: 88.362 + 13.397×weight_kg + 4.799×height_cm − 5.677×age. Females: 447.593 + 9.247×weight_kg + 3.098×height_cm − 4.330×age. Estimates basal metabolic rate from anthropometric data.

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