Sedentary (little or no exercise)
Lightly active (light exercise 1-3 days/week)
Moderately active (moderate exercise 3-5 days/week)
Very active (hard exercise 6-7 days/week)
Extra active (very hard exercise & physical job)
Basal Metabolic Rate (BMR):
0kcal/day
Total Daily Energy Expenditure (TDEE):
0kcal/day
*Based on the Mifflin-St Jeor Equation
Understanding Your Metabolic Rate
Your metabolic rate is essentially the number of calories your body burns to function. When people ask "What's my metabolic rate?", they are usually looking for two distinct numbers: their Basal Metabolic Rate (BMR) and their Total Daily Energy Expenditure (TDEE).
Basal Metabolic Rate (BMR)
Your BMR is the amount of energy (calories) your body needs to maintain basic physiological functions while at rest. This includes breathing, circulating blood, controlling body temperature, and cell growth. It accounts for about 60-70% of the calories you burn daily. Think of this as the "coma calories"—what you would burn if you did nothing but lay in bed all day.
Total Daily Energy Expenditure (TDEE)
While BMR is your baseline, TDEE represents the total calories you burn in a 24-hour period, factoring in your physical activity level. This calculator uses your BMR and multiplies it by an activity factor to determine your TDEE. This is the most practical number to use for weight management.
How Is It Calculated?
This calculator utilizes the Mifflin-St Jeor Equation, which is considered one of the most accurate formulas for estimating BMR in clinical settings. The formula is as follows:
Men: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Once the BMR is established, it is multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (extra active) to find your TDEE.
Using Your Results for Goals
Knowing your metabolic rate provides a mathematical roadmap for weight control:
Maintenance: To maintain your current weight, consume the number of calories listed as your TDEE.
Weight Loss: To lose weight, a common approach is to create a deficit of 300-500 calories below your TDEE.
Weight Gain: To build muscle or gain mass, aim for a surplus of 250-500 calories above your TDEE.
Remember that metabolic rate is dynamic. As you lose weight, your BMR decreases because there is less body mass to support. Conversely, building muscle can slightly increase your resting metabolic rate.
function calculateMetabolism() {
// Get input values
var gender = document.getElementById('gender').value;
var age = parseFloat(document.getElementById('age').value);
var weightInput = parseFloat(document.getElementById('weight').value);
var weightUnit = document.getElementById('weightUnit').value;
var heightInput = parseFloat(document.getElementById('height').value);
var heightUnit = document.getElementById('heightUnit').value;
var activityLevel = parseFloat(document.getElementById('activity').value);
// Validation
if (isNaN(age) || isNaN(weightInput) || isNaN(heightInput)) {
alert("Please enter valid numbers for age, weight, and height.");
return;
}
if (age < 0 || weightInput < 0 || heightInput < 0) {
alert("Values cannot be negative.");
return;
}
// Convert units to Metric (kg and cm) for the formula
var weightKg = weightInput;
var heightCm = heightInput;
if (weightUnit === 'lbs') {
weightKg = weightInput * 0.453592;
}
if (heightUnit === 'in') {
heightCm = heightInput * 2.54;
}
// Calculate BMR using Mifflin-St Jeor Equation
// Formula: (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + s
// s is +5 for males and -161 for females
var bmr = 0;
var baseCalc = (10 * weightKg) + (6.25 * heightCm) – (5 * age);
if (gender === 'male') {
bmr = baseCalc + 5;
} else {
bmr = baseCalc – 161;
}
// Calculate TDEE
var tdee = bmr * activityLevel;
// Display Results (Rounded to nearest whole number)
var bmrResult = Math.round(bmr);
var tdeeResult = Math.round(tdee);
document.getElementById('bmrResult').innerText = bmrResult.toLocaleString();
document.getElementById('tdeeResult').innerText = tdeeResult.toLocaleString();
// Show results div
document.getElementById('results').style.display = 'block';
}