Basal Metabolic Rate (BMR) Calculator with Body Fat Percentage
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to perform basic life-sustaining functions, such as breathing, circulation, and cell production, while at rest. Knowing your BMR is crucial for understanding your daily caloric needs and for weight management. This calculator also incorporates body fat percentage to provide a more refined estimate, as muscle tissue burns more calories at rest than fat tissue.
Male
Female
Understanding Basal Metabolic Rate (BMR) and Body Fat
Your BMR represents the minimum energy expenditure required to keep your body functioning at rest. Factors like age, gender, weight, and height all influence this value. Generally, men have a higher BMR than women due to typically higher muscle mass. As we age, BMR tends to decrease.
Incorporating body fat percentage provides a more accurate picture because muscle is metabolically more active than fat. A person with a higher percentage of lean body mass will have a higher BMR than someone of the same weight but with a higher body fat percentage. This calculator uses the Mifflin-St Jeor equation, which is widely considered one of the most accurate BMR prediction formulas. For males, the formula is: BMR = (10 * weight in kg) + (6.25 * height in cm) – (5 * age in years) + 5. For females, the formula is: BMR = (10 * weight in kg) + (6.25 * height in cm) – (5 * age in years) – 161.
While BMR is your resting metabolic rate, your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor. This calculator focuses solely on BMR, but understanding your BMR is the first step in determining your overall caloric needs for weight management, muscle gain, or fat loss.
function calculateBMR() {
var gender = document.getElementById("gender").value;
var age = parseFloat(document.getElementById("age").value);
var weight = parseFloat(document.getElementById("weight").value);
var height = parseFloat(document.getElementById("height").value);
var bodyFatPercentage = parseFloat(document.getElementById("bodyFatPercentage").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
if (isNaN(age) || isNaN(weight) || isNaN(height) || isNaN(bodyFatPercentage)) {
resultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
if (age <= 0 || weight <= 0 || height <= 0 || bodyFatPercentage 100) {
resultDiv.innerHTML = "Please enter realistic values for age, weight, height, and body fat percentage.";
return;
}
var bmr = 0;
if (gender === "male") {
bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5;
} else { // female
bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161;
}
// Adjusting for body fat percentage (this is a simplified approach, more complex models exist)
// Lean Body Mass (LBM) in kg = Weight * (1 – Body Fat Percentage / 100)
// Adjusted BMR using LBM is not a standard calculation in Mifflin-St Jeor,
// but we can explain its importance. The primary BMR calculation remains the same.
var leanBodyMass = weight * (1 – bodyFatPercentage / 100);
var outputHTML = "