Understanding your body's energy needs is the first step towards effective weight management. Our Weight Loss Calculator helps you estimate the daily calorie intake required to reach your target weight, based on your current stats, activity level, and desired rate of weight loss.
How Does the Weight Loss Calculator Work?
This calculator uses established formulas to provide a personalized estimate:
Basal Metabolic Rate (BMR): This is the number of calories your body burns at rest to maintain basic bodily functions (breathing, circulation, cell production). We use the Mifflin-St Jeor equation, which is widely considered one of the most accurate BMR formulas.
Total Daily Energy Expenditure (TDEE): Your TDEE is your BMR multiplied by an activity factor. This accounts for the calories you burn through daily activities and exercise.
Calorie Deficit: To lose weight, you need to consume fewer calories than your body burns (a calorie deficit). Approximately 7,700 calories equate to 1 kilogram of body fat (or 3,500 calories for 1 pound). The calculator determines the daily deficit needed to achieve your desired weekly weight loss.
Target Daily Calorie Intake: By subtracting your daily calorie deficit from your TDEE, we estimate the daily calorie intake you should aim for to lose weight at your chosen pace.
Time to Target Weight: Based on your total weight loss goal and your daily calorie deficit, the calculator estimates how long it will take to reach your target weight.
Factors Influencing Weight Loss
Metabolism: Your BMR is influenced by age, gender, height, and current weight.
Activity Level: The more active you are, the more calories you burn, increasing your TDEE.
Diet Quality: While calorie counting is important, the nutritional quality of your food also plays a crucial role in satiety and overall health.
Consistency: Sustainable weight loss requires consistent effort over time.
Individual Variation: These calculations are estimates. Individual metabolic rates and responses to diet and exercise can vary.
Using the Calculator
Simply enter your details into the fields below. Be as accurate as possible for the best estimate. Remember, this tool provides guidance, and it's always recommended to consult with a healthcare professional or a registered dietitian before making significant changes to your diet or exercise routine.
kg
lbs
kg
cm
inches
Sedentary (little or no exercise)
Lightly Active (light exercise/sports 1-3 days/week)
Moderately Active (moderate exercise/sports 3-5 days/week)
Very Active (hard exercise/sports 6-7 days a week)
Extra Active (very hard exercise/physical job)
kg
lbs
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padding: 20px;
border-radius: 8px;
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.form-group input[type="number"],
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.calculator-result {
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color: red;
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margin-top: 10px;
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.disclaimer {
font-size: 0.9em;
color: #666;
margin-top: 15px;
}
// Function to update target weight unit display
function updateTargetWeightUnit() {
var weightUnit = document.getElementById("weightUnit").value;
document.getElementById("targetWeightUnitDisplay").textContent = weightUnit;
}
// Add event listener to current weight unit dropdown
document.addEventListener('DOMContentLoaded', function() {
document.getElementById("weightUnit").onchange = updateTargetWeightUnit;
updateTargetWeightUnit(); // Set initial unit on page load
});
function calculateWeightLoss() {
var currentWeight = parseFloat(document.getElementById("currentWeight").value);
var weightUnit = document.getElementById("weightUnit").value;
var targetWeight = parseFloat(document.getElementById("targetWeight").value);
var height = parseFloat(document.getElementById("height").value);
var heightUnit = document.getElementById("heightUnit").value;
var age = parseFloat(document.getElementById("age").value);
var genderMale = document.getElementById("genderMale").checked;
var genderFemale = document.getElementById("genderFemale").checked;
var activityLevel = document.getElementById("activityLevel").value;
var weeklyLoss = parseFloat(document.getElementById("weeklyLoss").value);
var lossUnit = document.getElementById("lossUnit").value;
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = ""; // Clear previous results
// — Input Validation —
if (isNaN(currentWeight) || currentWeight <= 0 ||
isNaN(targetWeight) || targetWeight <= 0 ||
isNaN(height) || height <= 0 ||
isNaN(age) || age 120 ||
isNaN(weeklyLoss) || weeklyLoss = currentWeight) {
resultDiv.innerHTML = "Target Weight must be less than Current Weight.";
return;
}
if (!genderMale && !genderFemale) {
resultDiv.innerHTML = "Please select your gender.";
return;
}
// — Unit Conversions to KG and CM for BMR calculation —
var currentWeightKg = (weightUnit === "lbs") ? currentWeight * 0.453592 : currentWeight;
var targetWeightKg = (weightUnit === "lbs") ? targetWeight * 0.453592 : targetWeight;
var heightCm = (heightUnit === "inches") ? height * 2.54 : height;
var weeklyLossKg = (lossUnit === "lbs") ? weeklyLoss * 0.453592 : weeklyLoss;
// — Calculate BMR (Basal Metabolic Rate) using Mifflin-St Jeor Equation —
var bmr;
if (genderMale) {
bmr = (10 * currentWeightKg) + (6.25 * heightCm) – (5 * age) + 5;
} else { // Female
bmr = (10 * currentWeightKg) + (6.25 * heightCm) – (5 * age) – 161;
}
// — Calculate TDEE (Total Daily Energy Expenditure) —
var activityFactor;
switch (activityLevel) {
case "sedentary":
activityFactor = 1.2;
break;
case "lightlyActive":
activityFactor = 1.375;
break;
case "moderatelyActive":
activityFactor = 1.55;
break;
case "veryActive":
activityFactor = 1.725;
break;
case "extraActive":
activityFactor = 1.9;
break;
default:
activityFactor = 1.55; // Default to moderately active
}
var tdee = bmr * activityFactor;
// — Calculate Calorie Deficit for Weight Loss —
var caloriesPerKgFat = 7700; // Approximately 7700 calories per kg of fat
var dailyDeficitNeeded = (weeklyLossKg * caloriesPerKgFat) / 7;
// — Calculate Target Daily Calorie Intake —
var targetCalories = tdee – dailyDeficitNeeded;
// — Safety check for minimum calorie intake —
var minCalories = genderMale ? 1500 : 1200; // General recommendations
var warningMessage = "";
if (targetCalories < minCalories) {
warningMessage = "Warning: Your calculated target daily calorie intake (" + targetCalories.toFixed(0) + " calories) is below generally recommended minimums (" + minCalories + " calories). Consuming too few calories can be detrimental to your health and metabolism. Consider reducing your desired weekly weight loss or consulting a healthcare professional.";
}
// — Calculate Time to Reach Target Weight —
var totalWeightToLoseKg = currentWeightKg – targetWeightKg;
var totalCaloriesToLose = totalWeightToLoseKg * caloriesPerKgFat;
var daysToTarget = totalCaloriesToLose / dailyDeficitNeeded;
var weeksToTarget = daysToTarget / 7;
var monthsToTarget = weeksToTarget / 4.345; // Average weeks in a month
// — Display Results —
var resultHTML = "
Your Weight Loss Plan:
";
resultHTML += "Estimated BMR (Basal Metabolic Rate): " + bmr.toFixed(0) + " calories/day";
resultHTML += "Estimated TDEE (Total Daily Energy Expenditure): " + tdee.toFixed(0) + " calories/day";
resultHTML += "To lose " + weeklyLoss.toFixed(1) + " " + lossUnit + " per week, you need a daily calorie deficit of approximately " + dailyDeficitNeeded.toFixed(0) + " calories.";
resultHTML += "Your Target Daily Calorie Intake: " + targetCalories.toFixed(0) + " calories/day";
if (weeksToTarget > 0) {
resultHTML += "Estimated Time to Reach Target Weight:";
if (weeksToTarget < 4) {
resultHTML += "" + daysToTarget.toFixed(0) + " days (" + weeksToTarget.toFixed(1) + " weeks)";
} else if (monthsToTarget < 12) {
resultHTML += "" + weeksToTarget.toFixed(1) + " weeks (" + monthsToTarget.toFixed(1) + " months)";
} else {
resultHTML += "" + (monthsToTarget / 12).toFixed(1) + " years";
}
} else {
resultHTML += "You are already at or below your target weight.";
}
resultHTML += warningMessage;
resultHTML += "This calculator provides an estimate. Individual results may vary. Always consult with a healthcare professional or registered dietitian before starting any new diet or exercise program.";
resultDiv.innerHTML = resultHTML;
}