Basal Metabolic Rate (BMR) Calculator – Lean Body Mass Method
Your Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to perform essential functions like breathing, circulation, and cell production while at rest. This calculator uses the Lean Body Mass (LBM) method, which is often considered more accurate as it accounts for the difference in metabolic activity between fat and lean tissue. Lean body mass includes muscle, bone, organs, and water.
Male
Female
Your Estimated BMR:
Understanding Your BMR
The BMR represents the baseline calorie expenditure of your body. To determine your Total Daily Energy Expenditure (TDEE), you would multiply your BMR by an activity factor that reflects your lifestyle. For example:
Sedentary (little or no exercise): BMR x 1.2
Lightly active (exercise 1-3 days/week): BMR x 1.375
Moderately active (exercise 3-5 days/week): BMR x 1.55
Very active (exercise 6-7 days/week): BMR x 1.725
Extra active (very intense exercise & physical job): BMR x 1.9
Knowing your BMR is a crucial first step in managing your weight, whether your goal is to lose, gain, or maintain it, by providing a foundation for calculating your daily calorie needs.
function calculateBMR() {
var weightKg = parseFloat(document.getElementById("weightKg").value);
var heightCm = parseFloat(document.getElementById("heightCm").value);
var age = parseInt(document.getElementById("age").value);
var gender = document.getElementById("gender").value;
var bodyFatPercent = parseFloat(document.getElementById("bodyFatPercent").value);
var bmrResultDiv = document.getElementById("bmrResult");
// Input validation
if (isNaN(weightKg) || isNaN(heightCm) || isNaN(age) || isNaN(bodyFatPercent) || weightKg <= 0 || heightCm <= 0 || age <= 0 || bodyFatPercent 100) {
bmrResultDiv.innerHTML = "Please enter valid numbers for all fields.";
return;
}
// Convert height from cm to meters
var heightM = heightCm / 100;
// Calculate Lean Body Mass (LBM) in kg
var lbmKg;
if (gender === "male") {
lbmKg = weightKg * (1 – (bodyFatPercent / 100));
} else { // female
lbmKg = weightKg * (1 – (bodyFatPercent / 100));
}
// Mifflin-St Jeor Equation for BMR (commonly used and accurate)
// This equation is modified slightly to use LBM as a base
// A common approach is to estimate BMR based on LBM and then adjust for other factors.
// For a direct LBM-based formula, often a simpler formula is used:
// BMR = 370 + (21.6 * LBM in kg) for men
// BMR = 370 + (21.6 * LBM in kg) for women (some sources use slightly different constants, like 370 for men and 300 for women, but LBM is the primary driver)
// Let's use a widely accepted formula that incorporates LBM more directly in its structure or by first calculating fat mass and subtracting.
// Alternative: Use Harris-Benedict or Mifflin-St Jeor and then adjust. The prompt asks for LBM *method*.
// A common LBM method uses LBM to estimate RMR (Resting Metabolic Rate) which is very close to BMR.
// Formula based on LBM:
// For Men: BMR = (21.6 * LBM) + 370
// For Women: BMR = (21.6 * LBM) + 370 (some variations exist for women, e.g., 300 + 21.6*LBM. We'll use the consistent 21.6 multiplier)
var bmr = 0;
if (gender === "male") {
bmr = (21.6 * lbmKg) + 370;
} else { // female
bmr = (21.6 * lbmKg) + 370; // Using the same multiplier for simplicity as LBM is the key variable. Some sources use 300 for women's intercept.
}
bmrResultDiv.innerHTML = Math.round(bmr) + " calories per day";
}
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