Sedentary (Office job, little exercise)
Lightly Active (1-3 days/week)
Moderately Active (3-5 days/week)
Very Active (6-7 days/week)
Super Active (Physical job + training)
Mild Weight Loss (0.25 kg/week)
Standard Weight Loss (0.5 kg/week)
Aggressive Weight Loss (0.75 kg/week)
Extreme Weight Loss (1 kg/week)
Please enter valid values for Age, Height, and Weight.
Maintenance Calories (TDEE):2,500
Daily Deficit Required:-500
Your Daily Target:2,000 kcal
*Projected date to reach goal depends on consistency.
Understanding How to Calculate a Calorie Deficit
Achieving weight loss is fundamentally a matter of energy balance. To lose weight, you must consume fewer calories than your body expends. This state is known as a calorie deficit. This calculator uses the scientifically validated Mifflin-St Jeor equation to estimate your caloric needs accurately.
Why is TDEE important?
TDEE stands for Total Daily Energy Expenditure. It represents the total number of calories you burn in a day through basic survival functions (BMR), daily movements, and deliberate exercise. To create a deficit, you must eat below your TDEE.
How the Calculation Works
The calculation process involves three specific steps based on the data you provide:
Step 1: Calculate BMR (Basal Metabolic Rate). This is the energy your body needs just to keep your heart beating and lungs breathing. We use your age, gender, height, and weight for this.
Step 2: Determine TDEE. We multiply your BMR by an "Activity Factor" ranging from 1.2 (sedentary) to 1.9 (athlete) to find your maintenance level.
Step 3: Apply the Deficit. Based on your selected goal, we subtract calories from your TDEE. Generally, a deficit of 500 calories per day results in approximately 0.5 kg (1.1 lbs) of weight loss per week.
Safe Weight Loss Standards
While it might be tempting to select the "Extreme" option, experts recommend a weight loss rate of 0.5 kg to 1 kg (1-2 lbs) per week. Drastically lowering your calorie intake can slow down your metabolism, lead to muscle loss, and cause nutritional deficiencies.
Example Calculation
Let's look at a realistic scenario using this calculator:
Profile: A 35-year-old male, 180 cm tall, weighing 90 kg.
Activity: Moderately Active (exercises 3-5 times a week).
Goal: Standard Weight Loss (0.5 kg/week).
The Math:
BMR: Approx 1,850 calories/day.
TDEE: 1,850 x 1.55 (Activity) = 2,867 calories/day to maintain weight.
By sticking to ~2,367 calories daily, this individual would theoretically lose about 0.5 kg of body fat per week without starving.
function calculateCalories() {
// 1. Get Input Values
var ageInput = document.getElementById('age');
var heightInput = document.getElementById('height');
var weightInput = document.getElementById('weight');
var activitySelect = document.getElementById('activity');
var goalSelect = document.getElementById('goal');
var genderMale = document.getElementById('gender_male');
var errorMsg = document.getElementById('error-message');
var resultsArea = document.getElementById('results-area');
// 2. Parse Values
var age = parseFloat(ageInput.value);
var height = parseFloat(heightInput.value);
var weight = parseFloat(weightInput.value);
var activityMultiplier = parseFloat(activitySelect.value);
// Goal value logic: 0.5kg/week ~ 500kcal deficit, 1kg ~ 1000kcal
// The select values correspond to kg per week.
// 1 kg of fat is approx 7700 kcal.
// 0.5kg/week = 3850 kcal/week = 550 kcal/day.
// For simplicity, standard approximation is 500kcal/day per 1lb (0.45kg) loss.
// We will use: kg_loss_per_week * 1100 (rough conversion for daily deficit)
// Or standard: 0.5kg -> 500kcal, 1kg -> 1000kcal.
// Let's refine the deficit math based on the select value
// The select value is an index essentially.
// 0.5 (Mild) -> 250 kcal
// 1.0 (Standard) -> 500 kcal
// 1.5 (Aggressive) -> 750 kcal
// 2.0 (Extreme) -> 1000 kcal
var intensityIndex = parseFloat(goalSelect.value);
var dailyDeficit = intensityIndex * 500;
// 3. Validation
if (isNaN(age) || isNaN(height) || isNaN(weight) || age <= 0 || height <= 0 || weight <= 0) {
errorMsg.style.display = 'block';
resultsArea.style.display = 'none';
return;
} else {
errorMsg.style.display = 'none';
}
// 4. Calculate BMR (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 = 0;
if (genderMale.checked) {
bmr = (10 * weight) + (6.25 * height) – (5 * age) + 5;
} else {
bmr = (10 * weight) + (6.25 * height) – (5 * age) – 161;
}
// 5. Calculate TDEE
var tdee = bmr * activityMultiplier;
// 6. Calculate Target Calories
var targetCalories = tdee – dailyDeficit;
// Safety check: Don't go below 1200 (women) or 1500 (men) generally,
// but for a raw calculator, we just display the number but warn if very low.
// For this specific output, we just show the math.
if (targetCalories < 1000) {
targetCalories = 1000; // Floor it for safety display
}
// 7. Format Numbers
var tdeeFormatted = Math.round(tdee).toLocaleString();
var deficitFormatted = Math.round(dailyDeficit).toLocaleString();
var targetFormatted = Math.round(targetCalories).toLocaleString();
// 8. Update DOM
document.getElementById('tdee-result').innerText = tdeeFormatted + " kcal";
document.getElementById('deficit-result').innerText = "-" + deficitFormatted + " kcal";
document.getElementById('target-result').innerText = targetFormatted + " kcal";
resultsArea.style.display = 'block';
}