Understanding the Mifflin-St Jeor Equation

Type your stats into any reputable calorie calculator and it is probably using the Mifflin-St Jeor equation. But what is it, and why did it replace the formula that came before it?

A formula built on modern data

In 1990, researchers Mifflin, St Jeor, and colleagues published a study in the American Journal of Clinical Nutrition that developed new BMR equations from 498 healthy adults — men and women of varied ages and body compositions. Their equations predicted resting metabolic rate more accurately than the older Harris-Benedict formula, which dated back to 1919 and was based on a much smaller, less diverse sample.

The equations

• Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
• Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Each term has a physical meaning: weight and height capture your body size (bigger bodies burn more), age captures the slow metabolic decline over the years, and the final constant accounts for the average difference in body composition between sexes.

Worked example

A 28-year-old woman, 62 kg, 162 cm: (620) + (1012.5) − (140) − 161 = 1,331 kcal/day at rest. Lightly active (×1.375), her TDEE is about 1,830 kcal/day — her maintenance target.

Its limitations

No formula sees your body composition. Two people at 80 kg can have very different muscle mass, and muscle burns more than fat at rest. Very muscular athletes often find Mifflin-St Jeor underestimates their needs; in that case the Katch-McArdle formula (which uses body-fat percentage) is a better fit. For most people, though, Mifflin-St Jeor remains the best balance of accuracy and simplicity.

How NutriCounter uses it

Our BMR/TDEE tool applies exactly these equations with standard activity multipliers, then translates the result into a daily calorie goal based on whether you want to lose, maintain, or gain. Try it, then verify with 2–3 weeks of real tracking — your own data always wins.