Sedentary (Little/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)
Mild Weight Loss (10% Deficit)
Weight Loss (20% Deficit)
Extreme Weight Loss (30% Deficit)
Basal Metabolic Rate (BMR): 0 kcal
Maintenance Calories (TDEE): 0 kcal
Daily Target for Weight Loss
0 kcal
function calculateDeficit() {
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 goalMultiplier = parseFloat(document.getElementById('goal').value);
var gender = document.querySelector('input[name="gender"]:checked').value;
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 * goalMultiplier;
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() + " kcal/day";
document.getElementById('calorie-result').style.display = 'block';
}
Understanding the Calorie Deficit: The Science of Weight Loss
A calorie deficit is the fundamental requirement for weight loss. Simply put, it occurs when you consume fewer calories than your body burns over a specific period. While the concept sounds simple, calculating the precise numbers requires an understanding of your metabolic rate and activity levels.
How This Calculator Works
Our calculator uses the Mifflin-St Jeor Equation, which is currently considered the most accurate formula for estimating Basal Metabolic Rate (BMR) for the general population. Here is the breakdown of the calculation process:
BMR (Basal Metabolic Rate): This is the number of calories your body needs to function at rest (breathing, circulating blood, cell production).
TDEE (Total Daily Energy Expenditure): This is your maintenance level. It multiplies your BMR by an activity factor (from sedentary to highly active).
The Deficit: To lose weight, we apply a percentage reduction (10%, 20%, or 30%) to your TDEE to ensure you are burning stored fat for energy.
Realistic Example of Calorie Tracking
Consider a 30-year-old male, weighing 90kg and standing 180cm tall, with a moderately active lifestyle. His stats might look like this:
BMR: ~1,885 calories
Maintenance (TDEE): ~2,922 calories
20% Weight Loss Deficit: ~2,338 calories
By consuming roughly 2,340 calories per day, this individual would create a deficit of approximately 580 calories daily, leading to a healthy weight loss of about 0.5kg (1lb) per week.
Three Pillars of a Successful Deficit
1. High Protein Intake
When you are in a calorie deficit, your body may look to break down muscle tissue for energy. Consuming adequate protein (roughly 1.6g to 2.2g per kg of body weight) helps preserve lean muscle mass and keeps you feeling full longer.
2. Resistance Training
Lifting weights or performing bodyweight exercises signals to your body that it needs to keep its muscle. This ensures that the weight you lose comes primarily from body fat stores, improving your body composition.
3. Consistency Over Perfection
Weight loss is a marathon, not a sprint. A moderate 20% deficit is usually sustainable for several months, whereas an extreme 30%+ deficit may lead to fatigue, hormonal imbalances, and eventual "yo-yo" dieting.
Frequently Asked Questions
Is a 500-calorie deficit enough?
Yes. A 500-calorie daily deficit typically results in roughly 0.5kg (1lb) of weight loss per week. This is widely considered the "sweet spot" for sustainable progress.
What happens if I eat below my BMR?
While occasional days below BMR are not dangerous, consistently eating below your BMR for long periods can lead to metabolic adaptation, where your body slows down its processes to conserve energy, potentially stalling weight loss.