Formula A vs Formula B
Formula A (Mifflin-St Jeor) is the default for this calculator and works well for most people. It uses your age, sex, height, and weight to estimate your basal metabolic rate (BMR). It does not require knowing your body fat percentage and has strong research backing across a wide population.
Formula B (Katch-McArdle) uses lean body mass to estimate BMR. It can be more accurate for trained individuals who have estimated or measured their body fat percentage. If your body fat estimate is inaccurate, however, Formula B can be less accurate than Formula A.
When to use Formula A: When you do not know your body fat percentage, or when you are not confident in your estimate. It works well for most people.
When to use Formula B: When you have a reasonably accurate body fat estimate — from DEXA, calipers, or consistent progress photos — and you want a more individualized calculation.
For most users, the difference between the two formulas is small. If you switch formulas and the numbers change significantly, it usually means the body fat input needs refinement. Neither formula is a perfect measurement — both are estimates based on population averages.
References
- A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition (1990)
- Body composition via Katch-McArdle style lean-mass estimation. Exercise Physiology: Energy, Nutrition, and Human Performance (1996)
Related in “How the tools & numbers work”
- Integrated Calculator Flow
- How Daily Activity Affects Calories
- Why Step Count Matters
- How Activity Levels Work
- How Macro Targets Are Calculated
Use it in the app: open Learn inside BodEvo — free, local-first, no account required.