BMR Calculator
Basal Metabolic Rate Reference Tool
Enter your details to estimate the number of calories your body burns at rest.
Parameters
Basal Metabolic Rate
| Mifflin-St Jeor | -- |
| Revised Harris-Benedict | -- |
| Katch-McArdle | -- |
Understanding Basal Metabolic Rate (BMR)
Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic life-sustaining functions — breathing, circulation, cell production, and organ function — while completely at rest. It typically accounts for 60-75% of total daily calorie burn.
Body Composition
Muscle tissue burns more calories at rest than fat tissue, so a higher lean body mass raises BMR even at the same total body weight.
Age
BMR gradually declines with age as muscle mass naturally decreases, which is one reason calorie needs shift over a lifetime.
Sex
Males typically have a higher BMR than females of the same age and weight, largely due to a higher average proportion of muscle mass.
Genetics & Hormones
Thyroid function and inherited metabolic traits can shift BMR up or down independent of the body-composition factors this calculator can measure.
The Mifflin-St Jeor Equation
Men
Women
Where w is weight in kg, h is height in cm, and a is age in years. Published in 1990, Mifflin-St Jeor is considered the most accurate general-purpose BMR equation for modern populations, replacing the older Harris-Benedict formula from 1919 (revised in 1984).
Comparing the Three Formulas
| Formula | Inputs Used | Best For |
|---|---|---|
| Mifflin-St Jeor | Weight, height, age, sex | General population, most widely recommended today |
| Revised Harris-Benedict | Weight, height, age, sex | Historical comparison, slightly higher estimates |
| Katch-McArdle | Lean body mass (weight + body fat %) | People who know their body fat percentage, especially lean/muscular individuals |
Important Limitations
- Not a lab measurement: True BMR requires a controlled clinical setting (indirect calorimetry) — these formulas are population-based estimates.
- Doesn't include activity: BMR alone excludes movement, exercise, and digestion — see our TDEE Calculator for your full daily calorie burn.
- Medical conditions: Thyroid disorders, certain medications, and metabolic conditions can shift real BMR well outside formula-based estimates.
Key Takeaways
- BMR is your calorie floor. It represents energy burned at complete rest, before any activity is factored in.
- Mifflin-St Jeor is the modern standard. It's generally considered more accurate than the older Harris-Benedict equation for most people today.
- Body composition changes the picture. If you know your body fat percentage, Katch-McArdle can offer a more personalized estimate.
- Consult a professional. BMR is a baseline estimate — a registered dietitian or physician can refine it using metabolic testing (indirect calorimetry) if you have a condition affecting your metabolism.