Comprehensive Calculator Guide
This calculator works out your basal metabolic rate with the Katch-McArdle formula, which uses lean body mass rather than weight, height and age. At 80 kg and 20% body fat, lean mass is 64 kg and BMR is 370 + 21.6 × 64 = 1,752 kcal a day; with moderate activity you need about 2,716 kcal. It also shows the Cunningham formula for comparison.
Why lean mass
Most energy burned at rest goes to muscle and organs, not fat, so Katch-McArdle is more accurate for people who know their body fat, especially athletes. The result is only as good as the body-fat figure; DEXA or skinfolds by a professional beat home scales.
Multiply BMR by an activity factor, from 1.2 for sedentary to 1.9 for very active, to get daily needs. To lose weight gently, eat 300–500 kcal below that, and not below your BMR without medical supervision.
How to Use
- Enter your weight and body fat percentage.
- Choose your activity level.
- Press “Calculate BMR” to see both formulas and your daily needs.
Formula Used
LBM = weight × (1 − body fat) | Katch-McArdle = 370 + 21.6 × LBM | Cunningham = 500 + 22 × LBM | TDEE = BMR × activity
Practical Examples
- Example 1
- 80 kg, 20% fat, moderate: LBM 64 kg, BMR 1,752 kcal (Cunningham 1,908), TDEE 1,752 × 1.55 = 2,716.
- Example 2
- 62 kg, 28% fat, light: LBM 44.6 kg, BMR 1,334 kcal (Cunningham 1,482), TDEE about 1,835.
Important Tips
- Measure body fat the same way each time.
- Recalculate when your weight or body fat changes.
- Be honest about activity.
Common Mistakes to Avoid
- Guessing body fat.
- Treating BMR as total daily needs.
- Eating below BMR for long periods.
Frequently Asked Questions
- Katch-McArdle vs Mifflin?
- Mifflin uses weight, height, age and sex; Katch-McArdle uses lean mass only, so it suits people who know their body fat.
- How do I find my body fat?
- DEXA, bioimpedance scales or skinfold calipers; DEXA is the most accurate.
- Why is Cunningham higher?
- It assigns slightly more energy per kilogram of lean mass and is often used for very active athletes.