Which BMR formula is more accurate, Mifflin-St Jeor or Harris-Benedict?

Mifflin-St Jeor, according to the most widely cited comparison (Frankenfield et al., 2005), which found it predicted measured resting metabolic rate more accurately than Harris-Benedict across both normal-weight and obese adults. It's the formula this site's BMR calculator uses.

Why do the two formulas give different results for the same person?

Harris-Benedict was derived in 1919 from a small, non-representative sample and revised once in 1984. Mifflin-St Jeor was built in 1990 from a larger, more modern dataset and tends to run lower — often by 3-5% — reflecting that body composition and measurement methods have shifted since 1919.

Do both formulas need the same inputs?

Yes — both use weight, height, age, and sex, with no separate body-fat input. Neither accounts for muscle mass directly, which is why formulas that do use body-fat percentage (like Katch-McArdle) exist as a third option for people who know their body composition precisely.

Should I switch calculators if I've been using Harris-Benedict?

If you're tracking trends over time, consistency matters more than which formula you pick — switching formulas will shift your baseline number even if nothing about your body changed. If you're starting fresh, Mifflin-St Jeor is the better-supported default.

Guide

Mifflin-St Jeor vs. Harris-Benedict: which BMR formula wins?

Both formulas estimate the same number — calories burned at rest — and they don't agree, because one is nearly 90 years newer than the other.

By Buğra SözeriPublished September 25, 2026

Search “BMR formula” and you’ll run into two names: Harris-Benedict, from 1919 (revised in 1984), and Mifflin-St Jeor, from 1990. Plug the same weight, height, age, and sex into both and you’ll get two different calorie numbers — not because one is broken, but because they were built from different data, decades apart.

The two formulas, side by side

Formula	Men (kcal/day)	Women (kcal/day)
Mifflin-St Jeor (1990)	10×kg + 6.25×cm − 5×age + 5	10×kg + 6.25×cm − 5×age − 161
Harris-Benedict (revised 1984)	13.397×kg + 4.799×cm − 5.677×age + 88.362	9.247×kg + 3.098×cm − 4.330×age + 447.593

For a 35-year-old woman, 65 kg, 165 cm: Mifflin-St Jeor gives 10×65 + 6.25×165 − 5×35 − 161 = 650 + 1,031.25 − 175 − 161 = 1,345.25 kcal/day. Harris-Benedict gives 9.247×65 + 3.098×165 − 4.330×35 + 447.593 ≈ 1,433 kcal/day — an 88-calorie gap for identical inputs, roughly 6.5% apart.

Why Mifflin-St Jeor became the default

Harris-Benedict was derived from a study of roughly 239 people, measured with early-20th-century equipment, in a population that doesn’t reflect modern body composition or lifestyle. Mifflin-St Jeor was built from a larger, more contemporary sample using indirect calorimetry, the direct method of measuring resting energy expenditure from oxygen consumption.

The most-cited head-to-head comparison, Frankenfield, Roth-Yousey & Compher (2005), tested both formulas against measured resting metabolic rate in non-obese and obese adults and found Mifflin-St Jeor the most accurate of the equations tested. That's the reason dietitians and most modern calculators, including this BMR calculator, default to it over Harris-Benedict.

What neither formula accounts for

Both equations use only weight, height, age, and sex — neither directly measures muscle mass, which burns more calories at rest than fat tissue does. Two people with identical height, weight, age, and sex but very different body composition (say, an athlete vs. someone with a higher body-fat percentage) will get the same BMR estimate from either formula, even though their true resting metabolism likely differs. A formula like Katch-McArdle, which takes lean body mass directly, addresses this gap but requires knowing your body-fat percentage accurately, which most people don’t. For nearly everyone without that measurement, Mifflin-St Jeor remains the more practical, better-validated starting point. This is general educational information, not medical advice — for personalized calorie guidance, talk to a registered dietitian or your doctor.

Frequently asked questions

Which BMR formula is more accurate, Mifflin-St Jeor or Harris-Benedict?: Mifflin-St Jeor, according to the most widely cited comparison (Frankenfield et al., 2005), which found it predicted measured resting metabolic rate more accurately than Harris-Benedict across both normal-weight and obese adults. It's the formula this site's BMR calculator uses.
Why do the two formulas give different results for the same person?: Harris-Benedict was derived in 1919 from a small, non-representative sample and revised once in 1984. Mifflin-St Jeor was built in 1990 from a larger, more modern dataset and tends to run lower — often by 3-5% — reflecting that body composition and measurement methods have shifted since 1919.
Do both formulas need the same inputs?: Yes — both use weight, height, age, and sex, with no separate body-fat input. Neither accounts for muscle mass directly, which is why formulas that do use body-fat percentage (like Katch-McArdle) exist as a third option for people who know their body composition precisely.
Should I switch calculators if I've been using Harris-Benedict?: If you're tracking trends over time, consistency matters more than which formula you pick — switching formulas will shift your baseline number even if nothing about your body changed. If you're starting fresh, Mifflin-St Jeor is the better-supported default.

Sources & references

Authoritative references cited by this piece. Verified by Buğra Sözeri on the dates shown and re-checked at every deploy.

Frankenfield, Roth-Yousey & Compher, J Am Diet Assoc 2005 — Comparison of Predictive Equations for Resting Metabolic Rate — The systematic review finding Mifflin-St Jeor the most accurate predictive equation for non-obese and obese adults(as of 2026-09-25)
Mifflin, St Jeor et al., Am J Clin Nutr 1990 — A New Predictive Equation for Resting Energy Expenditure in Healthy Individuals — The original 1990 paper introducing the Mifflin-St Jeor equation(as of 2026-09-25)