§ · Katch–McArdle
Katch–McArdleBMR calculator.
Body-fat-aware BMR. Plug in weight + body-fat %, optionally pick an activity level for TDEE. Same formula BiteDeck's forecast uses on-device.
§ · Calculator
Body-fat-aware BMRBMR = 370 + 21.6 × LBM kg, where LBM = weight × (1 − bodyFat/100)
§ 01 · The formula, named
BMR = 370 + (21.6 × LBM kg), where LBM (lean body mass) = weight × (1 − bodyFat/100).
The 370 is a baseline metabolic floor. The 21.6 multiplier is the energy cost per kg of lean tissue — primarily muscle and organ mass. Fat tissue is much less metabolically active, so by zeroing it out the formula gets closer to your real resting energy expenditure than weight-only formulas.
§ 02 · When Katch–McArdle beats Mifflin–St Jeor
Mifflin–St Jeoruses total body weight. It works fine for most people, but it can't distinguish between two people of the same weight where one is lean and the other isn't.
Katch–McArdle works in lean mass directly. That matters most at the tails of body composition — for very lean athletes (Mifflin under-estimates) and for higher body fat (Mifflin over-estimates). If you train regularly, Katch–McArdle is usually closer to the truth.
§ 03 · Don't have a body-fat percentage?
Use the US Navy body fat calculator — three or four circumference measurements get you a usable estimate in two minutes. Plug the result back into this calculator.
Or, if you have a recent BMI, the Deurenberg formula (built into BiteDeck's app, alongside US Navy) gives a rough estimate without measurements.
§ 04 · How BiteDeck uses this
The forecast inside BiteDeck runs Katch–McArdle daily — using your saved body-fat % and the latest weight reading from HealthKit. The 5-state model (locked / unlocked / goal-reached / maintaining / reversed) sits on top of that BMR. See On-device weight forecasting for the rest of the wiring.
For comparison with the body-mass-aware approach: Mifflin–St Jeor TDEE calculator.