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Best BMR Formula: Which One Should You Use?

Three formulas, three slightly different answers. Instead of just explaining the math, here’s a straight recommendation based on your body type and what you actually know about yourself.

🕑 6 min read 🔄 Updated 3 August 2026

The Quick Recommendation

1
Most people, most of the time: use Mifflin-St Jeor. It’s the formula modern dietitians default to because it’s been validated as the most accurate on average across the general population.
2
If you know your body fat percentage and are lean or muscular: use Katch-McArdle instead. It’s built from lean body mass directly, which better reflects an athletic build that standard weight-based formulas can underestimate or overestimate.
3
If you just want to sanity-check a number or are curious about the classic clinical formula: Harris-Benedict is fine as a reference point, but expect it to run slightly higher than Mifflin-St Jeor.

Decision Table

Your SituationBest FormulaWhy
Average body composition, no body fat % knownMifflin-St JeorMost accurate on average for the general population
Lean, muscular or athletic build, body fat % knownKatch-McArdleUses lean body mass directly, avoiding fat-mass overestimation
Higher body fat percentageMifflin-St JeorWeight-based formulas tend to be more reliable here than lean-mass-only ones without accurate body fat data
Comparing against older clinical literatureHarris-BenedictThe historical reference formula, still cited in some older studies

Why Mifflin-St Jeor Wins by Default

Published in 1990 and re-validated repeatedly since, Mifflin-St Jeor was specifically designed to correct known overestimation issues in Harris-Benedict (a 1919 formula, revised in 1984). Across large validation studies, Mifflin-St Jeor consistently comes closer to measured resting energy expenditure for the general adult population, which is why it’s the default formula on this calculator and in most modern dietetics practice.

The trade-off with Katch-McArdle: it’s only as good as your body fat percentage input. A rough or inaccurate body fat estimate (from a hand-held scale, for instance) can make Katch-McArdle less reliable than simply using Mifflin-St Jeor with your actual weight.

How Different Are the Numbers, Really?

For someone with an average body composition, the gap between formulas is usually under 5–10%. For a very lean, muscular individual, Mifflin-St Jeor can meaningfully underestimate BMR because it doesn’t know how much of their weight is muscle — that’s the exact gap Katch-McArdle is designed to close.

Frequently Asked Questions

Only if your body fat percentage input is accurate. For most people without a precise body fat measurement, Mifflin-St Jeor remains the more reliable default.
Harris-Benedict is an older formula from 1919 that's known to slightly overestimate BMR compared to more recent validation data.
Yes, but for consistency it's best to stick with one formula when tracking changes over time, since switching formulas alone can shift your number independent of any real change.
Clinical settings sometimes use indirect calorimetry for precision, but Mifflin-St Jeor is widely used in dietetics practice as the standard formula-based estimate.

Try Both Formulas Yourself

Our calculator supports Mifflin-St Jeor by default, with an advanced Katch-McArdle option if you know your body fat percentage.

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