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)
Please enter valid positive numbers for all fields.
Your Basal Metabolic Rate (BMR)
0 Calories/day
This is the energy your body needs just to exist at rest.
Total Daily Energy Expenditure (TDEE)
Maintenance Calories:0 Calories/day
Mild Weight Loss (-0.25kg/week):0 Calories/day
Weight Loss (-0.5kg/week):0 Calories/day
Extreme Weight Loss (-1kg/week):0 Calories/day
How to Calculate Body Metabolic Rate (BMR)
Your Basal Metabolic Rate (BMR) is the number of calories your body burns while it is completely at rest. Even when you are sleeping or sitting still, your body requires energy to perform vital functions such as breathing, circulating blood, controlling body temperature, and cell growth.
Understanding your BMR is the starting point for any weight management plan. Once you know your BMR, you can estimate your Total Daily Energy Expenditure (TDEE), which determines how many calories you need to eat to maintain, lose, or gain weight based on your lifestyle.
The Calculation Formula
This calculator uses the Mifflin-St Jeor Equation, widely considered by health professionals to be the most accurate standard for calculating BMR. The formulas differ slightly for men and women:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Factors Influencing Your Metabolic Rate
Several variables impact your metabolic rate, which is why the calculator requires specific inputs:
Muscle Mass: Muscle requires more energy to maintain than fat. Individuals with higher muscle mass generally have a higher BMR.
Age: As you age, you naturally lose muscle mass and your metabolism slows down.
Gender: Men typically have less body fat and more muscle mass than women of the same age and weight, resulting in a higher BMR.
Genetics: Some people naturally have a faster or slower metabolism due to hereditary factors.
Understanding Activity Multipliers
While BMR tells you what you burn at rest, you do not spend all day sleeping. To find your actual daily calorie needs (TDEE), your BMR is multiplied by an activity factor:
Sedentary (1.2): Desk job, little to no intentional exercise.
Lightly Active (1.375): Light exercise or sports 1-3 days a week.
Moderately Active (1.55): Moderate exercise or sports 3-5 days a week.
Very Active (1.725): Hard exercise or sports 6-7 days a week.
Extra Active (1.9): Very hard exercise, physical job, or training twice a day.
Using These Numbers for Weight Goals
Once you have your TDEE (Maintenance Calories), you can adjust your intake to meet your goals. To lose approximately 1 lb (0.45 kg) of fat per week, a caloric deficit of about 500 calories per day is generally recommended. Conversely, to gain muscle, a surplus of 250-500 calories combined with resistance training is effective.
function toggleUnits() {
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var metricInputs = document.getElementById('metric-inputs');
var imperialInputs = document.getElementById('imperial-inputs');
var selectedValue = 'metric';
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imperialInputs.style.display = 'none';
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metricInputs.style.display = 'none';
imperialInputs.style.display = 'block';
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}
function calculateBMR() {
// Hide error message initially
var errorMsg = document.getElementById('error-message');
errorMsg.style.display = 'none';
// Inputs
var gender = document.getElementById('gender').value;
var age = parseFloat(document.getElementById('age').value);
var activityMultiplier = parseFloat(document.getElementById('activity').value);
var unitSystem = '';
var radios = document.getElementsByName('unitSystem');
for (var i = 0; i < radios.length; i++) {
if (radios[i].checked) unitSystem = radios[i].value;
}
var weightKg = 0;
var heightCm = 0;
// Logic to get weight and height based on unit system
if (unitSystem === 'metric') {
weightKg = parseFloat(document.getElementById('weightKg').value);
heightCm = parseFloat(document.getElementById('heightCm').value);
} else {
var wLbs = parseFloat(document.getElementById('weightLbs').value);
var hFt = parseFloat(document.getElementById('heightFt').value);
var hIn = parseFloat(document.getElementById('heightIn').value);
// Validation for imperial inputs before conversion
if (isNaN(wLbs) || isNaN(hFt) || isNaN(hIn)) {
errorMsg.style.display = 'block';
return;
}
// Conversion
weightKg = wLbs / 2.20462;
heightCm = ((hFt * 12) + hIn) * 2.54;
}
// Validation for common inputs
if (isNaN(age) || isNaN(weightKg) || isNaN(heightCm) || age <= 0 || weightKg <= 0 || heightCm <= 0) {
errorMsg.style.display = 'block';
return;
}
// Mifflin-St Jeor Equation
// 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
var bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age);
if (gender === 'male') {
bmr = bmr + 5;
} else {
bmr = bmr – 161;
}
// Calculate TDEE
var tdee = bmr * activityMultiplier;
// Update UI
document.getElementById('bmr-result').innerHTML = Math.round(bmr).toLocaleString() + ' Calories/day';
document.getElementById('tdee-result').innerText = Math.round(tdee).toLocaleString() + ' Calories/day';
// Weight Loss Estimates
document.getElementById('loss-mild').innerText = Math.round(tdee * 0.90).toLocaleString() + ' Calories/day'; // Roughly 10% deficit
document.getElementById('loss-normal').innerText = Math.round(tdee – 500).toLocaleString() + ' Calories/day'; // 500 cal deficit
document.getElementById('loss-extreme').innerText = Math.round(tdee – 1000).toLocaleString() + ' Calories/day'; // 1000 cal deficit
// Safety check: Don't show dangerous calorie levels (below 1200 generally unsafe without supervision)
var extremeVal = tdee – 1000;
if (extremeVal < 1200) {
document.getElementById('loss-extreme').innerHTML = "Not Recommended";
}
// Show result area
document.getElementById('result-area').style.display = 'block';
// Scroll to results
document.getElementById('result-area').scrollIntoView({ behavior: 'smooth' });
}