Mifflin-St Jeor Equation: Formula, Calculation, Accuracy, and Examples

Calculating your calorie needs can become confusing fast. You may find a BMR number online but still wonder what it actually means. Is it your maintenance intake, your daily calorie burn, or simply the energy your body uses at rest? Different calculators can also show different results, making the process even harder.

The Mifflin-St Jeor Equation provides a useful starting point. It estimates resting energy expenditure (REE) from your weight, height, age, and sex. Then, that estimate can be used with an activity factor to estimate TDEE. However, it is a prediction, not a direct measurement of your metabolism. The original study was based on 498 healthy adults and used indirect calorimetry to measure REE. (PubMed [1])

What Is the Mifflin-St Jeor Equation?

The Mifflin-St Jeor Equation is a mathematical formula developed to predict resting energy expenditure. In simple terms, REE estimates the energy your body uses while resting.

The original 1990 study included 251 men and 247 women aged 19–78. Both normal-weight and obese adults were included. Therefore, the equation was developed from a broader adult sample than many older formulas.

Although many websites call the result BMR, the original research specifically developed the equation for REE. BMR and RMR are related concepts, but they are not technically identical. Read more in our TDEE vs BMR Guide.

Mifflin-St Jeor Formula

The equation uses specific mathematical constants for men and women:

These simplified formulas come directly from the original research. The researchers found that simplifying the original coefficients did not reduce predictive value. Estimate your baseline instantly with our BMR Calculator.

What the Coefficients Mean

In multiple linear regression modeling (Mifflin et al., 1990; n = 498 healthy subjects), the numbers in the equation represent empirical regression weights that mathematically minimize prediction error across the measured population, rather than direct physiological meters of organ surface area or endocrine decline:

Because these numbers are statistical regression coefficients, individual metabolic variance (such as high athletic muscularity or endocrine factors) can cause actual measured REE to deviate from calculated estimates by approximately ±8% to 10%.

How to Calculate It

First, make sure your measurements use the correct units. Weight must be in kilograms (kg), while height must be in centimeters (cm).

Importantly, neither number represents maintenance calories. Instead, both are resting estimates.

How Does It Become TDEE?

Your body uses energy for more than resting functions. Physical activity, exercise, and digestion also contribute to daily energy expenditure. Consequently, TDEE is higher than your resting estimate for most people.

Typical calculator activity multiplier factors include:

For example, an estimated REE of 1,780 calories multiplied by 1.55 gives about 2,759 calories per day on our homepage TDEE Calculator.

However, these factors are broad estimates. Two people in the same activity category can have different jobs, step counts, workouts, and daily movement. As a result, calculated TDEE can differ from actual energy expenditure. Learn more in our How to Calculate TDEE Guide.

Is the Mifflin-St Jeor Equation Accurate?

Research supports the formula as a useful general prediction equation. A systematic review by the Academy of Nutrition and Dietetics found that Mifflin-St Jeor predicted measured RMR within ±10% in more non-obese and obese adults than the other commonly used equations examined. (PubMed [1])

Even so, individual accuracy is not guaranteed. One study found that accuracy varied by factors such as BMI, age, sex, and race or ethnicity. Moreover, research in older adults found that no prediction equation consistently provided accurate and precise results for every individual.

Therefore, the result should be treated as an estimate, not an exact laboratory measurement.

Why Can Your Result Differ?

Different calculators may use different formulas, activity factors, rounding methods, or assumptions. For instance, one tool may use Mifflin-St Jeor while another uses Harris-Benedict.

The original Mifflin study found that the older Harris-Benedict equation (1919/1984) overestimated measured REE by about 5% in its study sample. Later evidence also found Mifflin-St Jeor to perform well among commonly used equations.

Nevertheless, that does not mean it is automatically more accurate for every single person.

Mifflin-St Jeor vs. Katch-McArdle

Katch-McArdle uses lean body mass, while Mifflin-St Jeor uses total weight, height, age, and biological sex.

Therefore, someone with reliable body-composition data (such as DEXA scans) may consider a lean-mass-based equation like Katch-McArdle. However, using more information does not automatically guarantee better accuracy. Prediction performance depends on the individual and population being studied.

Common Calculation Mistakes

For this reason, check every input before using the final number.

What Does the Result Tell You?

The calculation gives you a starting point for understanding your energy needs. Next, the estimate can be used to calculate TDEE. After that, TDEE can help you understand maintenance calories on our Maintenance Calorie Calculator and plan a suitable target on our Calorie Deficit Calculator.

In contrast, the equation does not directly measure your individual metabolism, exercise calories, exact maintenance intake, or exact weight-loss calories.

Real-world results matter, too. If your calculated maintenance level does not match your observed weight trend over time, the estimate may need adjustment.

Frequently Asked Questions

The Bottom Line

The Mifflin-St Jeor Equation is a practical way to estimate resting energy expenditure using four basic inputs: weight, height, age, and sex. Its original research and later systematic reviews support its usefulness, while also showing that prediction errors can occur at the individual level. (PubMed [1])

For that reason, use the result as a starting point rather than an exact metabolic measurement. Estimate your resting needs, calculate TDEE, and then compare the estimate with real-world scale changes over time. That approach makes the calculation more useful while respecting its scientific limitations.

Methodology and Sources

This article uses the original 1990 Mifflin-St Jeor study as the primary source for the formula and its development. Later systematic reviews and validation studies were used to explain accuracy, population differences, and limitations.

The goal is to explain both how the equation works and how to interpret it responsibly. In particular, the article distinguishes a calculated estimate from a directly measured value, helping readers use the number as a practical starting point rather than treating it as an exact result.

• Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990 Feb;51(2):241-7. (PubMed [1])
• Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc. 2005.

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