Sedentary (Office job, little exercise)
Lightly Active (1-3 days/week)
Moderately Active (3-5 days/week)
Very Active (6-7 days/week)
Extra Active (Physical job + intense training)
Mild Weight Loss (250 kcal/day)
Standard Weight Loss (500 kcal/day)
Aggressive Weight Loss (750 kcal/day)
Extreme Weight Loss (1000 kcal/day)
Your Basal Metabolic Rate (BMR): calories/day
Daily Maintenance Calories (TDEE): calories/day
Your Target Daily Intake: calories/day
Estimated Weekly Weight Loss: kg
Understanding Calorie Deficit: The Key to Weight Loss
A calorie deficit occurs when you consume fewer calories than your body needs to maintain its current weight. This fundamental principle of thermodynamics forces your body to use stored energy (usually fat) to make up the difference, resulting in weight loss over time.
How the Calculation Works
This calculator uses the Mifflin-St Jeor Equation, widely considered the most accurate formula for estimating metabolic rates in healthy adults. The process involves three distinct steps:
BMR (Basal Metabolic Rate): The energy your body burns at rest to maintain vital functions like breathing and heartbeat.
TDEE (Total Daily Energy Expenditure): Your BMR multiplied by an activity factor that accounts for movement and exercise.
The Deficit: Subtracting your chosen calorie goal from your TDEE to find your target intake.
Example Calculation
Imagine a 35-year-old male, 180cm tall, weighing 90kg with a moderately active lifestyle:
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
Choosing the Right Deficit
While it may be tempting to choose an "Extreme" deficit, health professionals generally recommend a deficit of 500 calories per day to lose approximately 0.5kg (1 lb) per week. This rate is sustainable and helps preserve muscle mass while targeting body fat.
Warning: It is generally not recommended for women to consume fewer than 1,200 calories per day or men to consume fewer than 1,500 calories per day without medical supervision.
function calculateCalories() {
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 activity = parseFloat(document.getElementById("activity").value);
var deficit = parseFloat(document.getElementById("deficit").value);
var resultsDiv = document.getElementById("calc-results");
if (isNaN(age) || isNaN(weight) || isNaN(height)) {
alert("Please enter valid numbers for age, weight, and height.");
return;
}
var bmr = 0;
if (gender === "male") {
bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5;
} else {
bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161;
}
var tdee = bmr * activity;
var target = tdee – deficit;
var weeklyLoss = (deficit * 7) / 7700; // 7700 kcal is roughly 1kg of fat
if (target < 1000) {
target = 1000; // Safety floor for the display
}
document.getElementById("res-bmr").innerHTML = Math.round(bmr).toLocaleString();
document.getElementById("res-tdee").innerHTML = Math.round(tdee).toLocaleString();
document.getElementById("res-target").innerHTML = Math.round(target).toLocaleString();
document.getElementById("res-loss").innerHTML = weeklyLoss.toFixed(2);
resultsDiv.style.display = "block";
resultsDiv.scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}