Sedentary (Little or no exercise)
Lightly Active (1-3 days/week)
Moderately Active (3-5 days/week)
Very Active (6-7 days/week)
Extra Active (Physical job + training)
Lose 0.5 kg (1.1 lbs) per week
Lose 0.75 kg (1.6 lbs) per week
Lose 1.0 kg (2.2 lbs) per week
Calculation Results
Maintenance Calories (TDEE): kcal/day
Target Deficit Calories: kcal/day
*These results are estimates based on the Mifflin-St Jeor equation. Consult a doctor before starting a new diet program.
function calculateDeficit() {
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 deficitAmount = parseFloat(document.getElementById('deficitGoal').value);
if (isNaN(age) || isNaN(weight) || isNaN(height)) {
alert("Please fill in all fields with valid numbers.");
return;
}
var bmr;
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 targetCalories = tdee – deficitAmount;
// Health safety check: Generally don't recommend under 1200 (women) or 1500 (men)
if (targetCalories < 1200 && gender === 'female') {
targetCalories = 1200;
} else if (targetCalories < 1500 && gender === 'male') {
targetCalories = 1500;
}
document.getElementById('tdeeResult').innerText = Math.round(tdee).toLocaleString();
document.getElementById('deficitResult').innerText = Math.round(targetCalories).toLocaleString();
document.getElementById('resultsArea').style.display = 'block';
document.getElementById('resultsArea').scrollIntoView({ behavior: 'smooth' });
}
How to Use the Calorie Deficit Calculator
A calorie deficit occurs when you consume fewer calories than your body requires to maintain its current weight. This deficit forces your body to use stored energy (body fat) for fuel, resulting in weight loss. To calculate your deficit accurately, you need to understand two key metrics: BMR and TDEE.
The Science Behind the Calculation
Our calculator uses the Mifflin-St Jeor Equation, widely considered the most accurate formula for calculating Basal Metabolic Rate (BMR) for the general population. Here is how the numbers work:
BMR (Basal Metabolic Rate): The number of calories your body burns at complete rest just to keep your organs functioning.
TDEE (Total Daily Energy Expenditure): Your BMR multiplied by an activity factor (1.2 to 1.9) representing your movement throughout the day.
Deficit: Subtracting calories (usually 500-1000) from your TDEE to reach your goals.
Realistic Example
Let's look at a typical scenario for a 35-year-old male:
Weight: 95 kg
Height: 180 cm
Activity: Lightly active (TDEE = ~2,600 kcal)
Goal: 0.5 kg loss per week (500 kcal deficit)
Target Calories: 2,100 kcal per day
Tips for Sustainable Weight Loss
While 1 kg per week is possible, most health experts recommend a steady loss of 0.5 kg per week. This ensures you are losing fat rather than muscle mass. Additionally, always prioritize high-protein foods to help preserve lean muscle tissue while in a caloric deficit.
Important Safety Note: It is generally not recommended for women to drop below 1,200 calories or men below 1,500 calories per day without medical supervision. Extremely low-calorie diets can lead to nutrient deficiencies and metabolic slowdown.