Sedentary (Little or no exercise)
Lightly Active (Exercise 1-3 days/week)
Moderately Active (Exercise 3-5 days/week)
Very Active (Hard exercise 6-7 days/week)
Extra Active (Very hard exercise & physical job)
Your Daily Calorie Results
Maintenance (Keep current weight):–
Mild Weight Loss (0.25 kg/week):–
Weight Loss (0.5 kg/week):–
Extreme Weight Loss (1 kg/week):–
* Note: Consumption below 1,200 (women) or 1,500 (men) calories should be supervised by a medical professional.
function calculateCalories() {
var gender = document.getElementById('calcGender').value;
var age = parseFloat(document.getElementById('calcAge').value);
var weight = parseFloat(document.getElementById('calcWeight').value);
var height = parseFloat(document.getElementById('calcHeight').value);
var activity = parseFloat(document.getElementById('calcActivity').value);
if (isNaN(age) || isNaN(weight) || isNaN(height) || age <= 0 || weight <= 0 || height <= 0) {
alert("Please enter valid positive numbers for age, weight, and height.");
return;
}
// BMR Calculation (Mifflin-St Jeor Equation)
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 maintenance = bmr * activity;
// Deficits based on 7700 kcal per 1kg loss (approx 3500 kcal per 1lb)
// 0.25kg/week = ~275 kcal deficit/day
// 0.5kg/week = ~550 kcal deficit/day
// 1kg/week = ~1100 kcal deficit/day
var mildLoss = maintenance – 275;
var weightLoss = maintenance – 550;
var extremeLoss = maintenance – 1100;
document.getElementById('resMaintenance').innerText = Math.round(maintenance).toLocaleString() + " kcal";
document.getElementById('resMild').innerText = Math.round(mildLoss).toLocaleString() + " kcal";
document.getElementById('resLoss').innerText = Math.round(weightLoss).toLocaleString() + " kcal";
document.getElementById('resExtreme').innerText = Math.round(extremeLoss).toLocaleString() + " kcal";
document.getElementById('calcResults').style.display = 'block';
// Show safety warning if any target is too low
var threshold = (gender === 'male') ? 1500 : 1200;
if (extremeLoss < threshold || weightLoss < threshold) {
document.getElementById('safetyWarning').style.display = 'block';
} else {
document.getElementById('safetyWarning').style.display = 'none';
}
}
How Your Calorie Needs Are Calculated
Understanding weight loss requires a balance between energy intake (food) and energy expenditure (metabolism and activity). This calculator uses the Mifflin-St Jeor Equation, widely considered by dietitians to be the most accurate standard for predicting Basal Metabolic Rate (BMR).
The Science of Deficit
To lose weight, you must consume fewer calories than your body burns. This is known as a calorie deficit. Generally, a deficit of 500 to 1,000 calories per day will lead to a safe weight loss of approximately 0.5 to 1 kilogram per week.
BMR (Basal Metabolic Rate): The calories your body burns at rest to maintain vital functions like breathing and heart rate.
TDEE (Total Daily Energy Expenditure): Your BMR multiplied by your activity level. This is your maintenance number.
The Deficit: Subtracting calories from your TDEE to force your body to use stored fat for energy.
Realistic Example
Imagine a 35-year-old male weighing 90kg at 180cm tall with a sedentary lifestyle:
BMR: ~1,850 kcal/day.
Maintenance (TDEE): 1,850 x 1.2 = 2,220 kcal/day.
To Lose 0.5kg Weekly: He should target ~1,720 kcal/day (a 500-calorie deficit).
Safety and Sustainability
While "Extreme Weight Loss" results are shown, it is rarely sustainable or healthy for long periods. Rapid weight loss can lead to muscle loss and nutrient deficiencies. For long-term success, focus on high-protein intake and strength training to preserve lean muscle while losing fat.