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 or 2x training)
function calculateCalorieDeficit() {
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 (!age || !weight || !height || age <= 0 || weight <= 0 || height <= 0) {
alert('Please enter valid positive numbers for age, weight, and height.');
return;
}
// Mifflin-St Jeor Equation
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 targetIntake = tdee – deficitAmount;
// 7700 calories roughly equals 1kg of body fat
var weeklyLoss = (deficitAmount * 7) / 7700;
document.getElementById('bmrVal').innerText = Math.round(bmr).toLocaleString();
document.getElementById('tdeeVal').innerText = Math.round(tdee).toLocaleString();
document.getElementById('targetVal').innerText = Math.round(targetIntake).toLocaleString();
document.getElementById('lossVal').innerText = weeklyLoss.toFixed(2);
document.getElementById('deficitResult').style.display = 'block';
// Safety Check
if (targetIntake < 1200 && gender === 'female') {
alert('Warning: Your target intake is below 1,200 calories. Consuming too few calories can be dangerous. Please consult a professional.');
} else if (targetIntake < 1500 && gender === 'male') {
alert('Warning: Your target intake is below 1,500 calories. Consuming too few calories can be dangerous. Please consult a professional.');
}
}
Understanding the Calorie Deficit for Effective Weight Loss
A calorie deficit is the fundamental requirement for losing weight. It occurs when you consume fewer calories than your body burns to maintain its current weight. This calculator uses the Mifflin-St Jeor Equation, widely considered the most accurate formula for calculating Basal Metabolic Rate (BMR) in non-clinical settings.
How Your Results Are Calculated
The calculation involves three primary steps:
BMR (Basal Metabolic Rate): The number of calories your body burns at rest to maintain vital functions like breathing and heart rate.
TDEE (Total Daily Energy Expenditure): Your BMR multiplied by an activity factor. This represents the total calories you burn in a typical day.
The Deficit: By subtracting your chosen deficit (e.g., 500 calories) from your TDEE, we determine the daily energy intake required to force your body to use stored fat for fuel.
Real-World Example
Imagine a 35-year-old male, 180cm tall, weighing 90kg with a moderately active lifestyle.
His calculated BMR might be roughly 1,880 calories.
His TDEE (Maintenance) would be approximately 2,914 calories.
To lose 0.5kg per week, he would aim for a 500-calorie deficit, meaning a daily intake of 2,414 calories.
Sustainable Weight Loss Tips
While it is tempting to choose the "Extreme Deficit" option, health experts recommend a moderate deficit of 300 to 500 calories per day. This usually results in a weight loss of 0.25kg to 0.5kg per week. Losing weight too quickly can lead to muscle loss, nutritional deficiencies, and a "yo-yo" effect where the weight is quickly regained.
Always prioritize high-protein foods and resistance training during a deficit to ensure that the weight you lose comes from fat stores rather than lean muscle mass.