Mifflin-St Jeor vs. Harris-Benedict: Which BMR Formula Should You Trust?
Two formulas, decades apart, both estimate the same number — but they were built from different people, and it shows.
Where each formula came from
The Harris-Benedict equation dates to 1919, derived from a relatively small study population, and was revised in 1984 to correct for some of its original biases. The Mifflin-St Jeor equation followed in 1990, built from a larger and more demographically representative sample, reflecting body compositions closer to the modern population. Both estimate Basal Metabolic Rate (BMR) — the calories your body burns at complete rest — from just age, sex, height, and weight.
The formulas side by side
Mifflin-St Jeor (men): 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Mifflin-St Jeor (women): 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Harris-Benedict (men): 88.362 + 13.397 × weight(kg) + 4.799 × height(cm) − 5.677 × age
Harris-Benedict (women): 447.593 + 9.247 × weight(kg) + 3.098 × height(cm) − 4.330 × age
Why they disagree
For most people, Harris-Benedict tends to estimate a slightly higher BMR than Mifflin-St Jeor — typically within about 5%, though the gap can widen for people at higher body weights, since Harris-Benedict was built on a population with less data at those weights. Mifflin-St Jeor is more widely cited in modern clinical and nutrition research as the more accurate general-purpose formula, which is why most calorie-tracking tools default to it. Harris-Benedict still shows up often enough, especially in older references, that it's worth knowing rather than dismissing.
What neither formula accounts for
Both formulas work from just four inputs and can't capture things that meaningfully affect metabolism: muscle mass versus fat mass, genetics, thyroid function, or health conditions. Two people with identical age, sex, height, and weight can have real BMRs that differ by a meaningful margin. Treat either formula's output as a reasonable starting estimate to plan around, not a measured fact about your body — and adjust based on how your actual weight trends over a few weeks.
Calculate both
The BMR Calculator shows both formulas side by side for your numbers. For total daily calorie needs including activity, see the Calorie Calculator.