What is the most accurate formula for BMR?

December 19, 2025 •

3 min read

According to a 2005 study, the Mifflin-St Jeor equation is more likely than other formulas to predict resting metabolic rate (RMR) within 10% of the measured value. While no single predictive equation is perfect for everyone, the Mifflin-St Jeor equation is widely considered to be the most accurate formula for BMR for the general population.

Quick Summary

The Mifflin-St Jeor equation is the most reliable formula for estimating Basal Metabolic Rate (BMR) for most healthy adults. It uses weight, height, age, and sex to calculate resting energy expenditure. For individuals with low body fat, the Katch-McArdle formula, which requires lean body mass, can be more precise.

Key Points

Mifflin-St Jeor is Most Accurate: The Mifflin-St Jeor equation is generally considered the most reliable formula for calculating BMR in the general population, based on modern research.
Harris-Benedict is Outdated: The older Harris-Benedict formula often overestimates BMR and is less accurate, particularly in modern, less active individuals.
Katch-McArdle is Best for Lean Individuals: For very lean or athletic individuals, the Katch-McArdle formula, which is based on lean body mass, can provide a more precise BMR estimate.
Predictive Formulas are Estimates: All BMR formulas are estimates and should be used as a starting point; they are not as precise as clinical measurements via indirect calorimetry.
BMR Influenced by Many Factors: Your BMR is influenced by age, sex, weight, height, genetics, and body composition. For instance, muscle mass burns more calories at rest than fat tissue.
BMR is Just the First Step: To determine your total daily calorie needs, you must multiply your calculated BMR by an activity factor that reflects your daily exercise and movement.

Understanding Basal Metabolic Rate (BMR)

Basal Metabolic Rate, or BMR, represents the amount of energy your body expends at complete rest to maintain vital functions like breathing, blood circulation, and cell production. It is the single largest component of most people's total daily energy expenditure (TDEE), accounting for approximately 60-75% of the total calories you burn. Understanding your BMR is a foundational step in any weight management strategy, providing a baseline from which to plan your calorie intake for weight loss, maintenance, or gain.

The Most Accurate Predictive Formula: Mifflin-St Jeor

For the vast majority of healthy adults, the Mifflin-St Jeor equation is the most accurate and widely recommended formula for estimating BMR. Developed in 1990, it offers a more reliable prediction than older formulas and is praised for its balance of accuracy and accessibility.

Here are the specific formulas for both men and women, using metric measurements:

For men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5
For women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161

The Case for Katch-McArdle: Focusing on Lean Body Mass

While the Mifflin-St Jeor formula is excellent for the general population, the Katch-McArdle formula may be more accurate for highly athletic individuals or those with a very low body fat percentage. This formula estimates Resting Daily Energy Expenditure (RDEE) by factoring in lean body mass (LBM). The Katch-McArdle formula is RDEE = 370 + (21.6 × Lean Body Mass in kg). It requires an accurate body fat percentage measurement to determine LBM, which is less accessible than simple weight and height measurements.

A Comparison of BMR Formulas

Comparing the Mifflin-St Jeor equation with the older Harris-Benedict formula highlights why the former is preferred. The Harris-Benedict formula, from 1919, often overestimates BMR in modern populations.


Feature	Mifflin-St Jeor	Revised Harris-Benedict	Katch-McArdle
Development Year	1990	1984 (revised)	Published in 1980s
Primary Factor	Weight, Height, Age, Sex	Weight, Height, Age, Sex	Lean Body Mass (LBM)
Best For	General population	Older formula, less accurate for modern populations	Lean, muscular individuals
Accuracy	Consistently high	Often overestimates RMR by 7–24%	Can be the most accurate if LBM is known precisely
Key Metric	BMR (Basal)	BMR (Basal)	RDEE (Resting)
Data Needs	Weight (kg), Height (cm), Age (years), Sex	Weight (kg), Height (cm), Age (years), Sex	Lean Body Mass (kg) or Body Fat %

Limitations of Predictive Equations

All predictive equations for BMR are estimates, limited by inherent factors and the data they were derived from. Accuracy can be affected by individual variations, certain medical conditions, and ethnicity not fully represented in the original studies. The most precise BMR measurement is achieved through indirect calorimetry in a clinical setting, but predictive formulas are a practical alternative for most people.

How to Choose and Use the Right Formula

For most individuals, begin with the Mifflin-St Jeor equation due to its reliability and accessibility. Once BMR is calculated, multiply it by an activity factor to determine Total Daily Energy Expenditure (TDEE), which is a better indicator of total daily calorie needs. If you are very lean and seeking greater precision, the Katch-McArdle formula with accurate body fat measurement may be more suitable. Regardless of the formula, these are starting points. Monitoring progress and adjusting intake are essential. Consulting a registered dietitian or healthcare provider is recommended for advanced guidance.

Conclusion

The Mifflin-St Jeor equation is the most accurate and practical formula for calculating BMR for the majority of the population. Its use of readily available metrics and proven reliability make it the preferred choice for estimating resting caloric needs. The Katch-McArdle formula offers a powerful alternative for individuals with specific body compositions, though it requires more complex data. Both equations provide a valuable foundation for effective weight management strategies.

Frequently Asked Questions

The primary difference lies in their accuracy and the data used for their creation. The Harris-Benedict formula is older and tends to overestimate BMR, whereas the Mifflin-St Jeor formula, developed later with more modern data, provides a more reliable and accurate estimate, especially for people with obesity.

You should use the Katch-McArdle formula if you are very lean and muscular and can accurately measure your body fat percentage. It's more precise for individuals with atypical body composition because it focuses on lean body mass, which is more metabolically active than fat.

To calculate your TDEE, you multiply your BMR by an activity factor. For example, a sedentary person would multiply their BMR by 1.2, while a very active person might use 1.725 or 1.9.

Different online calculators may use different formulas (Mifflin-St Jeor, Harris-Benedict, etc.), leading to varying results. The Mifflin-St Jeor is generally considered the most accurate for the average person, but results can still differ slightly based on which equation is used.

Yes, you can increase your BMR, primarily by increasing your lean muscle mass through regular strength training. Muscle tissue is more metabolically active than fat, so more muscle means you burn more calories at rest.

For nearly perfect accuracy, BMR must be measured clinically using a method called indirect calorimetry. This involves measuring gas exchange (oxygen consumption and carbon dioxide production) under strict, resting conditions.

Yes, crash dieting or severely restricting calories can slow your metabolism to conserve energy, a process known as metabolic adaptation. This can lower your BMR, making it harder to lose weight over time.