Two equations that estimate BMR from the same inputs, published 70 years apart. They usually land within a few percent of each other — but one is the modern default for a reason.
| Mifflin-St Jeor | Harris-Benedict (revised) | |
|---|---|---|
| Published | 1990 | 1919 (revised 1984) |
| Inputs | Weight, height, age, sex | Weight, height, age, sex |
| Accuracy (general population) | Higher in modern studies | Slightly less accurate |
| Needs body fat? | No | No |
| Best for | Default for most people | Comparison / legacy use |
Both estimate basal metabolic rate from the same four inputs, so for most people they produce numbers within a few percent of each other. The difference is in the coefficients: Harris-Benedict (the original 1919 equation, revised in 1984) tends to run slightly higher, while Mifflin-St Jeor was derived from a more modern population.
When researchers compared the common equations against measured resting energy, Mifflin-St Jeor predicted it more accurately for most people. That's why it's the default here and across most reputable calculators. Harris-Benedict is still useful as a comparison point and appears in older material.
Both are height/weight formulas, so neither can account for unusual body composition. If you have a reliable body-fat measurement, the lean-mass-based Katch-McArdle formula can beat both. Our BMR calculator lets you switch between all three and compare them on your own numbers.
Mifflin-St Jeor for most people — it's the most accurate validated equation without a body-fat measurement. Use Katch-McArdle if you have a reliable body-fat percentage.
Different coefficients derived from different populations decades apart. Harris-Benedict usually reads a little higher. For most people the gap is small.