CALCULATOR

Mifflin-St Jeor Calculator

The equation most dietetics guidance now favours, with all three common formulas shown side by side so you can see how much they disagree.

Result

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BMR–

Daily burn at your activity–

Mifflin-St Jeor–

Harris-Benedict–

Katch-McArdle–

Spread between them–

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The Mifflin-St Jeor equation

Mifflin-St Jeor was published in 1990 and has become the default equation for estimating resting energy expenditure in healthy adults. It was derived from a larger and more contemporary population than Harris-Benedict, and comparison studies have generally found it more accurate for the general population, which is why most dietetics guidance now favours it.

It uses weight, height, age and sex, with no body composition input. That makes it usable by anyone with a tape measure and a scale, and also means it cannot distinguish a muscular person from a sedentary one of the same size.

Expect an error band of roughly ten percent in either direction. That is not a flaw in the equation so much as an unavoidable consequence of predicting individual metabolism from four variables.

The equation

Mifflin-St Jeor (1990)Men: BMR = (10 x W) + (6.25 x H) - (5 x A) + 5
Women: BMR = (10 x W) + (6.25 x H) - (5 x A) - 161

W = weight in kg, H = height in cm, A = age in years

Worked examples

Person	Calculation	BMR
Man, 80 kg, 175 cm, 30	800 + 1094 - 150 + 5	1,749 kcal
Woman, 65 kg, 165 cm, 30	650 + 1031 - 150 - 161	1,370 kcal
Man, 95 kg, 180 cm, 50	950 + 1125 - 250 + 5	1,830 kcal
Woman, 55 kg, 160 cm, 25	550 + 1000 - 125 - 161	1,264 kcal

Turning BMR into a calorie target

Activity	Multiplier	BMR 1,749 becomes
Sedentary	1.2	2,099 kcal
Light	1.375	2,405 kcal
Moderate	1.55	2,711 kcal
Active	1.725	3,017 kcal
Very active	1.9	3,323 kcal

The multiplier introduces far more uncertainty than the equation. Moving one step up the table changes the result by roughly 300 kcal, which dwarfs the difference between BMR formulas. Most people overestimate their activity level, and that single choice explains the majority of cases where a calculator seems wrong.

Frequently asked questions

Is Mifflin-St Jeor the most accurate BMR formula?

For the general population, comparison studies generally favour it over Harris-Benedict. For lean, trained people who know their body fat percentage, Katch-McArdle tends to perform better.

What is the Mifflin-St Jeor formula?

Men: 10W + 6.25H - 5A + 5. Women: 10W + 6.25H - 5A - 161, with weight in kg, height in cm and age in years.

Why does my result differ from other calculators?

Most differences come from the activity multiplier rather than the equation. Multiplier choice moves the final figure far more than the BMR calculation does.

Should I eat my BMR?

No. BMR is rest only. Multiply by an activity factor for maintenance, then apply a deficit or surplus to that.

Sources

Mifflin MD, St Jeor ST et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. Journal of the American Dietetic Association, 2005.
National Institutes of Health, Office of Dietary Supplements. Nutrient fact sheets. ods.od.nih.gov
NHS. Nutrition and health guidance. nhs.uk
US Departments of Agriculture and Health and Human Services. Dietary Guidelines for Americans, 2025-2030. dietaryguidelines.gov

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General information, not medical advice. Consult a qualified professional before changing your diet, especially with a medical condition.