Katch-McArdle Calculator for Bodybuilders & Lifters

The problem with a size-only calorie formula is that it cannot tell muscle from fat. Two men at 100 kg get the same estimate from Mifflin-St Jeor even if one is a lean lifter at 12% body fat and the other carries far more fat — yet the lifter's extra muscle burns real energy the formula never sees. That systematic under-count is why serious trainees reach for Katch-McArdle: it starts from lean body mass, so every kilogram of muscle you have built is reflected in the number. The catch is that it needs an honest body fat percentage, so measure it consistently — calipers, a DEXA scan, or the Body Fat % Calculator — rather than guessing low.

Every target below is just your maintenance figure plus or minus a number. Work a lifter at 100 kg and 12% body fat through it: 88 kg of lean mass gives a BMR near 2,271 kcal, and a very-active factor of 1.725 puts maintenance around 3,917 kcal.

These are calculated numbers, not instructions — the scale and the mirror settle the argument. If your weight isn't moving the way the target predicts over two to three weeks, adjust the calories, not the formula. The Calorie Deficit Calculator maps a cut out week by week.

The quiet advantage of knowing your lean mass is that you can set protein off lean tissue rather than total weight — the method that best preserves muscle in a deficit. For the 88 kg-lean lifter above, roughly 1.9 to 2.3 grams per kilogram of lean mass is about 167 to 202 grams of protein a day. Feed the rest of your calories into the Macro Calculator to fix carbs and fat. One habit matters most: recalculate as your composition changes. Lean mass and maintenance both shift as you cut or grow, so re-run the numbers every 4–5 kg (about 10 lb) of body-weight change rather than trusting a figure from three months ago.