BMR Calculator

Compare resting energy needs. Computes basal metabolic baseline across Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle models.

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Calculate BMR Values

Enter your biological measurements on the left to see your resting metabolism comparison.

Table of Contents

1. What is Basal Metabolic Rate (BMR)?

Basal Metabolic Rate (BMR) represents the minimum amount of caloric energy your body needs to maintain basic life-sustaining functions (e.g. breathing, blood circulation, cellular repair) at complete rest in a temperate environment.

Your BMR represents the largest component of your daily energy expenditure, typically accounting for **60% to 75%** of your Total Daily Energy Expenditure (TDEE). Understanding your resting metabolism is critical for setting target calorie goals, as it represents the energy your body requires simply to exist.

2. Mifflin-St Jeor vs Harris-Benedict Equations

Our calculator computes resting metabolic rate using three standard clinical equations:

  • Mifflin-St Jeor: Validated as a highly accurate predictor of resting metabolic rate in healthy adults. It uses weight, height, and age parameters.
  • Harris-Benedict: An older model revised in 1984 by Roza and Shizgal to improve accuracy. It tends to yield slightly higher estimates than the Mifflin equation.

3. The Role of Lean Mass (Katch-McArdle Model)

The **Katch-McArdle formula** is highly accurate because it bases its calculation on **Lean Body Mass (LBM)** rather than total body weight. This is particularly useful for muscular individuals, as muscle tissue is more metabolically active than fat tissue at rest.

To use this model, you must provide your body fat percentage, which is used to separate fat mass from lean weight: BMR = 370 + 21.6 × Lean Mass (kg).

4. Factors That Influence Resting Metabolism

Several physiological factors influence your BMR:

  • Lean Muscle Mass: Building muscle increases your resting metabolic rate, as muscle tissue burns more calories at rest than fat tissue. Check your targets with our Macro Calculator.
  • Biological Sex: Men typically have higher BMRs than women of the same weight, primarily due to having higher percentages of lean muscle tissue on average.
  • Age: BMR naturally decreases with age, primarily due to the loss of lean muscle mass (sarcopenia) that occurs if active lifestyle habits are not maintained.