Mifflin–St Jeor vs Katch–McArdle: Which BMR Formula Is More Accurate?

Estimating your calorie needs starts with calculating your Basal Metabolic Rate (BMR) — the number of calories your body burns at complete rest to maintain essential functions such as breathing, circulation, hormone production, and temperature regulation.

Two of the most widely used formulas for estimating BMR are:

• Mifflin–St Jeor Equation
• Katch–McArdle Formula

While both formulas aim to estimate daily energy expenditure, they work differently and are suited for different individuals.

Understanding when to use each formula can help you create more accurate calorie targets for:

• Weight loss
• Muscle gain
• Maintenance
• Athletic performance
• Body recomposition

What Is BMR?

Basal Metabolic Rate represents the minimum energy required for survival at rest. Your BMR accounts for approximately 60–75% of your Total Daily Energy Expenditure (TDEE).

Your total calorie needs are influenced by:

• Age
• Sex
• Height
• Weight
• Muscle mass
• Activity level
• Genetics
• Hormones

Since directly measuring metabolism requires laboratory equipment, BMR formulas provide estimates based on measurable variables.

The Mifflin–St Jeor Equation

The Mifflin–St Jeor Equation is considered one of the most accurate general-purpose BMR formulas for the average population.

It was developed in 1990 and has largely replaced the older Harris–Benedict equation in modern nutrition practice.

Formula for men:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5

Formula for women:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

This formula uses:

• Weight
• Height
• Age
• Biological sex

It does NOT account for body composition directly.

Advantages of Mifflin–St Jeor

• Well-validated in research
• Accurate for most people
• Easy to calculate
• No body fat measurement required
• Commonly used in calorie calculators

For the majority of people, this equation produces sufficiently accurate maintenance calorie estimates.

Limitations of Mifflin–St Jeor

Because the formula does not account for lean body mass, it may:

• Underestimate calories for muscular individuals
• Overestimate calories for individuals with high body fat percentages

Two people with the same height and weight may have very different muscle mass levels, which affects metabolism significantly.

The Katch–McArdle Formula

The Katch–McArdle Formula attempts to solve this limitation by incorporating lean body mass instead of total body weight.

Formula:

BMR = 370 + (21.6 × Lean Body Mass in kg)

Lean Body Mass (LBM):

LBM = Weight × (1 − Body Fat % ÷ 100)

Unlike Mifflin–St Jeor, this formula is:

• Gender-neutral
• Based on body composition
• More personalized

Because muscle tissue is metabolically active, individuals with more lean mass generally burn more calories at rest.

Advantages of Katch–McArdle

• More accurate for lean or muscular individuals
• Better for athletes and bodybuilders
• Accounts for body composition
• Useful during cutting and bulking phases

For example:

Two men both weigh 85 kg:

• Person A: 12% body fat
• Person B: 30% body fat

Even though their body weight is identical, Person A has substantially more lean mass and therefore likely burns more calories at rest.

Katch–McArdle reflects this difference more accurately.

Limitations of Katch–McArdle

The formula depends entirely on body fat percentage accuracy.

Many people estimate body fat incorrectly using:

• Visual comparisons
• Inaccurate smart scales
• Poor-quality online charts

Even small body fat estimation errors can significantly affect calorie calculations.

For example:

• Estimating 15% instead of 20% body fat changes lean mass calculations noticeably.

If body fat estimates are inaccurate, Mifflin–St Jeor may actually produce better real-world results.

Example Comparison

Example individual:

• Male
• 30 years old
• 180 cm
• 85 kg
• 15% body fat

Mifflin–St Jeor:

(10 × 85) + (6.25 × 180) − (5 × 30) + 5

= 1,830 kcal/day

Katch–McArdle:

Lean Body Mass = 85 × (1 − 0.15)

= 72.25 kg

BMR = 370 + (21.6 × 72.25)

= 1,931 kcal/day

Difference:

≈ 100 calories/day

For lean and muscular individuals, Katch–McArdle often estimates slightly higher calorie needs.

Which Formula Should You Use?

For most people:

• Use Mifflin–St Jeor

For athletes or individuals with reliable body fat measurements:

• Use Katch–McArdle

General recommendation:

Why Calorie Estimates Are Never Perfect

Even the best formulas are still estimates.

Real metabolism varies due to:

• Genetics
• Hormones
• Stress
• Sleep
• Medication
• Thyroid function
• Adaptive thermogenesis

Most formulas can vary:

±5–15% from actual energy expenditure.

That is why calorie calculators should be viewed as starting points rather than exact prescriptions.

The best approach:

1. Estimate calories

2. Track body weight for 2–3 weeks

3. Adjust intake based on real-world results

How to Improve Accuracy

To improve calorie estimation:

• Weigh yourself consistently
• Track food intake accurately
• Monitor weight trends, not daily fluctuations
• Prioritize protein intake
• Recalculate after major weight changes

Your body's response matters more than any formula.

FAQ: Mifflin vs Katch–McArdle

For most people, Mifflin–St Jeor is accurate enough. Katch–McArdle can be more precise for lean individuals with reliable body fat measurements.

Because it accounts for lean body mass. Individuals with more muscle typically burn more calories at rest.

Usually no. Most beginners do not have accurate body fat measurements, which reduces formula reliability.

Yes. All calorie equations are estimates and may differ from actual metabolism by 5–15% or more.

Use a formula as a starting point, then track your body weight and calorie intake over several weeks.

Most wearable devices use generalized algorithms and may not be highly accurate for calorie expenditure.

Most modern calculators use Mifflin–St Jeor by default because it performs well for the general population.