BMR Calculator with Body Fat Percentage: Katch-McArdle Accuracy (Not Just Weight-Based)

Most BMR Calculators Get It Wrong for Athletes

Standard BMR calculators use only weight, height, age, and gender. The problem? They treat muscle and fat as equal. That's wrong.

200 lbs at 12% body fat = 176 lbs of calorie-burning muscle. 200 lbs at 35% body fat = 130 lbs of calorie-burning muscle.

Same weight. Completely different metabolisms. A standard calculator gives both people the exact same BMR. Our calculator corrects this.

Katch-McArdle: BMR from Lean Body Mass

When you enter your body fat percentage, our BMR calculator uses the Katch-McArdle formula:

BMR = 370 + (21.6 × lean body mass in kg)

Your lean body mass is calculated directly from your weight and body fat %. The result is a BMR based on your actual muscle mass — not an average assumption.

We also compute Mifflin-St Jeor and average the two. The dual-formula approach is why our calculator is more accurate for anyone who knows their body fat percentage.

When Do You Need Body Fat-Based BMR?

A standard BMR calculator works fine for average body composition. But you need body fat-based BMR if you:

• Have more muscle than average (athlete, regular lifter)
• Have less muscle than average (sedentary, post-diet muscle loss)
• Are tracking body recomposition (building muscle while losing fat)
• Want precise calorie targets for a cut or bulk

If you do not know your body fat percentage yet, use our free body fat calculator first — takes 2 minutes with a tape measure.

From BMR to What You Actually Eat

Your BMR is just the baseline. Multiply it by your activity level to get your TDEE (Total Daily Energy Expenditure):

Our calculator shows all five, so you know exactly what to eat for cutting, maintenance, or bulking.

Calculate your true BMR: Free BMR Calculator with Body Fat →