Sedentary (Little or no exercise)
Lightly Active (Exercise 1-3 days/week)
Moderately Active (Exercise 3-5 days/week)
Very Active (Exercise 6-7 days/week)
Super Active (Physical job or 2x training)
Your Basal Metabolic Rate (BMR)
0 kcal/day
Daily Energy Expenditure (TDEE)
0 kcal/day
Calories needed based on activity:
Sedentary
–
Light Active
–
Moderate
–
Very Active
–
How to Calculate Basal Metabolic Rate Manually
Understanding your Basal Metabolic Rate (BMR) is the cornerstone of any effective weight management or nutrition plan. Whether your goal is weight loss, muscle gain, or simply maintaining your current physique, knowing your BMR helps you determine exactly how much energy your body needs just to exist.
What is BMR?
Basal Metabolic Rate represents the number of calories your body burns at complete rest to maintain vital functions such as breathing, blood circulation, cell production, and nutrient processing. It accounts for approximately 60-75% of your total daily energy expenditure.
The Calculation Formula
While there are several equations used to calculate BMR, the Mifflin-St Jeor Equation is widely considered the most accurate standard for the general population. This is the formula used in the calculator above.
Manual Calculation Steps
To calculate your BMR manually, follow the formula specific to your gender:
For Men:
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
For Women:
BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Example Calculation
Let's look at an example of how to calculate BMR manually for a 30-year-old female who weighs 65 kg and is 165 cm tall.
Your BMR is only the calories burned at rest. To find your Total Daily Energy Expenditure (TDEE)—the amount you burn in a real day—you must multiply your BMR by an activity factor:
Sedentary (1.2): Desk job, little exercise.
Lightly Active (1.375): Light exercise 1-3 days/week.
Moderately Active (1.55): Moderate exercise 3-5 days/week.
Very Active (1.725): Hard exercise 6-7 days/week.
Extra Active (1.9): Physical job or double training sessions.
Why Accuracy Matters
Calculating your BMR manually provides a solid baseline for nutrition planning. However, remember that these formulas are estimates based on averages. Factors like muscle mass (lean tissue burns more calories than fat), genetics, and hormonal health can influence your actual metabolic rate. It is generally recommended to start with the calculated TDEE, track your weight for 2-3 weeks, and adjust your calorie intake based on real-world results.
var currentUnit = 'metric';
function switchUnit(unit) {
currentUnit = unit;
var btnMetric = document.getElementById('btnMetric');
var btnImperial = document.getElementById('btnImperial');
var labelWeight = document.getElementById('labelWeight');
var groupMetric = document.getElementById('groupMetricHeight');
var groupImperial = document.getElementById('groupImperialHeight');
var weightInput = document.getElementById('weight');
if (unit === 'metric') {
btnMetric.className = 'unit-btn active';
btnImperial.className = 'unit-btn';
labelWeight.innerText = 'Weight (kg)';
weightInput.placeholder = '70';
groupMetric.classList.remove('hidden');
groupImperial.classList.add('hidden');
} else {
btnMetric.className = 'unit-btn';
btnImperial.className = 'unit-btn active';
labelWeight.innerText = 'Weight (lbs)';
weightInput.placeholder = '150';
groupMetric.classList.add('hidden');
groupImperial.classList.remove('hidden');
}
}
function calculateBMR() {
// Get Inputs
var age = parseFloat(document.getElementById('age').value);
var weight = parseFloat(document.getElementById('weight').value);
var genderElements = document.getElementsByName('gender');
var gender = 'male';
for (var i = 0; i < genderElements.length; i++) {
if (genderElements[i].checked) {
gender = genderElements[i].value;
break;
}
}
var activityMultiplier = parseFloat(document.getElementById('activity').value);
// Validate inputs
if (isNaN(age) || isNaN(weight) || age <= 0 || weight <= 0) {
alert("Please enter valid positive numbers for Age and Weight.");
return;
}
var weightInKg = weight;
var heightInCm = 0;
// Unit Conversion logic
if (currentUnit === 'imperial') {
// Convert Lbs to Kg
weightInKg = weight * 0.453592;
var ft = parseFloat(document.getElementById('heightFt').value);
var inc = parseFloat(document.getElementById('heightIn').value);
if (isNaN(ft)) ft = 0;
if (isNaN(inc)) inc = 0;
if (ft === 0 && inc === 0) {
alert("Please enter a valid height.");
return;
}
// Convert Height to Cm
var totalInches = (ft * 12) + inc;
heightInCm = totalInches * 2.54;
} else {
// Metric
heightInCm = parseFloat(document.getElementById('heightCm').value);
if (isNaN(heightInCm) || heightInCm <= 0) {
alert("Please enter a valid height in cm.");
return;
}
}
// Mifflin-St Jeor Equation
// P = 10m + 6.25h – 5a + s
var bmr = (10 * weightInKg) + (6.25 * heightInCm) – (5 * age);
if (gender === 'male') {
bmr = bmr + 5;
} else {
bmr = bmr – 161;
}
// Calculate TDEE
var tdee = bmr * activityMultiplier;
// Update UI
document.getElementById('resultBox').style.display = 'block';
document.getElementById('bmrResult').innerHTML = Math.round(bmr).toLocaleString() + ' kcal/day';
document.getElementById('tdeeResult').innerHTML = Math.round(tdee).toLocaleString() + ' kcal/day';
// Grid Update
document.getElementById('valSedentary').innerText = Math.round(bmr * 1.2).toLocaleString();
document.getElementById('valLight').innerText = Math.round(bmr * 1.375).toLocaleString();
document.getElementById('valModerate').innerText = Math.round(bmr * 1.55).toLocaleString();
document.getElementById('valVery').innerText = Math.round(bmr * 1.725).toLocaleString();
// Scroll to result
document.getElementById('resultBox').scrollIntoView({ behavior: 'smooth' });
}