Mifflin-St Jeor Calculator

What is the Mifflin-St Jeor calculator?

This calculator estimates your basal metabolic rate (BMR) using the Mifflin-St Jeor equation. Your BMR is the number of calories your body burns at complete rest to keep its core functions running — breathing, circulation, temperature regulation, and cell repair.

Enter your sex, weight, height, and age, and the calculator returns your BMR in calories per day. Measurements entered in pounds or inches are converted to kilograms and centimeters before the formula is applied.

A short history of the equation

The equation was published in 1990 by M. D. Mifflin and S. T. St Jeor, who re-derived resting energy expenditure from a study of healthy adults. It was developed to improve on older estimates such as the Harris-Benedict equation, and in many comparisons it predicts resting metabolism more accurately for modern populations, which is why it is widely used by dietitians today.

How does the calculator work?

The tool plugs your inputs into a single equation that has the same body for both sexes and differs only by a constant term:

• It uses your weight in kilograms, height in centimeters, and age in years.
• It adds a sex-specific constant: $+5$ for men and $-161$ for women.

The result is your estimated resting calorie burn for one day.

Formula

The Mifflin-St Jeor equation is:

where $w$ is weight in kilograms, $h$ is height in centimeters, $a$ is age in years, and $s$ is the sex constant — $+5$ for men and $-161$ for women.

Examples

Example 1: Man, 70 kg, 175 cm, 30 years

Estimated resting need: about 1648.75 calories per day.

Example 2: Woman, 70 kg, 175 cm, 30 years

Estimated resting need: about 1482.75 calories per day.

Practical notes

• BMR is an estimate. Actual resting energy use varies with body composition, genetics, hormones, and health conditions.
• To find your total daily calorie needs, multiply BMR by an activity factor; the BMR calculator with the Harris-Benedict equation does this step automatically.
• If you know your body fat percentage, the Katch-McArdle BMR calculator bases the estimate on lean body mass instead of total weight.
• Recalculate when your weight changes noticeably so the estimate stays useful.

FAQs

How accurate is the Mifflin-St Jeor equation?

For most healthy adults it gives a reliable estimate and is generally considered more accurate than the older Harris-Benedict equation, especially across a range of body weights.

Why does the men’s formula give a higher BMR?

The only difference between the sexes is the constant term: men get $+5$ and women get $-161$, reflecting average differences in body composition.

Can I use pounds and inches?

Yes. Enter your measurements in any supported unit and the calculator converts them to kilograms and centimeters before applying the formula.

What is the difference between BMR and TDEE?

BMR is the energy you burn completely at rest. Total daily energy expenditure (TDEE) is your BMR multiplied by an activity factor, so it is always higher. See the general BMR calculator for more context.