Mifflin-St Jeor vs. Katch-McArdle
Why body fat percentage matters for your BMR calculation.
The Quick Answer
Mifflin-St Jeor uses weight, height, age, and gender. Katch-McArdle uses lean body mass. For most people, the difference is less than 100 calories. Use Katch-McArdle only if you have an accurate body fat measurement (DEXA, hydrostatic). Otherwise, Mifflin-St Jeor is more practical and nearly as accurate.
The Two Main BMR Formulas
Mifflin-St Jeor Equation
Men: (10 × weight kg) + (6.25 × height cm) - (5 × age) + 5
Women: (10 × weight kg) + (6.25 × height cm) - (5 × age) - 161
- • Uses: Weight, height, age, gender
- • Accuracy: ±10% for most people
- • Best for: General population
- • Pros: Simple, no body fat needed
Katch-McArdle Formula
BMR = 370 + (21.6 × Lean Body Mass in kg)
- • Uses: Lean body mass only
- • Accuracy: ±8% if BF% is accurate
- • Best for: Athletes, bodybuilders
- • Pros: Accounts for body composition
Why Body Fat Percentage Changes Your BMR
The Science: Muscle vs. Fat
- • Muscle tissue: Burns ~6 calories per pound per day at rest
- • Fat tissue: Burns ~2 calories per pound per day at rest
- • Muscle is 3x more metabolically active than fat
Person A: 180 lbs, 15% body fat
- • Lean mass: 153 lbs
- • Fat mass: 27 lbs
- • Mifflin-St Jeor BMR: 1,850
- • Katch-McArdle BMR: 1,870
- • Difference: Only 20 calories
Person B: 180 lbs, 30% body fat
- • Lean mass: 126 lbs
- • Fat mass: 54 lbs
- • Mifflin-St Jeor BMR: 1,850
- • Katch-McArdle BMR: 1,590
- • Difference: 260 calories!
Same weight, different body composition = different calorie needs
When to Use Each Formula
Use Mifflin-St Jeor If:
- • You don't know your body fat percentage accurately
- • You're an average fitness enthusiast
- • You want a simple, reliable calculation
- • You're just starting your fitness journey
Use Katch-McArdle If:
- • You have an accurate body fat measurement (DEXA, hydrostatic)
- • You're a competitive athlete or bodybuilder
- • Your body composition is significantly different from average
- • You're very lean (under 10% men, under 18% women)
Real-World Accuracy Comparison
| Profile | Mifflin-St Jeor | Katch-McArdle | Difference |
|---|---|---|---|
| Average male (20% BF) | 1,800 cal | 1,780 cal | 20 cal |
| Average female (28% BF) | 1,450 cal | 1,420 cal | 30 cal |
| Lean athlete (10% BF) | 1,900 cal | 1,950 cal | 50 cal |
| Higher body fat (35% BF) | 1,800 cal | 1,550 cal | 250 cal |
For most people, the difference is negligible. Only extreme body compositions show significant variance.
Frequently Asked Questions
Which is more accurate: Mifflin-St Jeor or Katch-McArdle?
For most people, Mifflin-St Jeor is more practical and nearly as accurate. Katch-McArdle requires knowing your body fat percentage accurately. If you have reliable body fat data (DEXA scan), Katch-McArdle can be more precise for lean individuals. For average users, the difference is typically less than 100 calories.
Why does body fat percentage change my TDEE multiplier?
Body fat matters because muscle burns more calories than fat at rest. Two people at 180 lbs with different body compositions have different BMRs. The person with more muscle burns more calories even when doing nothing.