Losing Weight Calculator

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Scientific Weight Loss Calculator

Male Female
Sedentary (Office job, little 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 (Physical job + intense training)
0.25 kg (Steady) 0.5 kg (Recommended) 0.75 kg (Aggressive) 1.0 kg (Very Aggressive)

Your Weight Loss Results

function calculateWeightLoss() { var gender = document.getElementById("gender").value; var age = parseFloat(document.getElementById("age").value); var weight = parseFloat(document.getElementById("currentWeight").value); var height = parseFloat(document.getElementById("height").value); var activity = parseFloat(document.getElementById("activity").value); var targetWeight = parseFloat(document.getElementById("targetWeight").value); var weeklyRate = parseFloat(document.getElementById("weeklyRate").value); if (!age || !weight || !height || !targetWeight) { alert("Please fill in all fields correctly."); return; } if (targetWeight >= weight) { alert("Goal weight must be lower than current weight for weight loss calculation."); 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; // 7700 calories roughly equals 1kg of body fat var weeklyCaloricDeficit = weeklyRate * 7700; var dailyCaloricDeficit = weeklyCaloricDeficit / 7; var dailyTargetCalories = tdee – dailyCaloricDeficit; var totalWeightToLose = weight – targetWeight; var weeksToGoal = totalWeightToLose / weeklyRate; var monthsToGoal = weeksToGoal / 4.345; var resultDiv = document.getElementById("weightLossResult"); var resultContent = document.getElementById("resultContent"); var html = "Maintenance Calories (TDEE): " + Math.round(tdee) + " kcal/day"; html += "Daily Calorie Target for Loss: " + Math.round(dailyTargetCalories) + " kcal/day"; html += "
"; html += "Estimated Timeline:"; html += "
    "; html += "
  • Total to lose: " + totalWeightToLose.toFixed(1) + " kg
    • "; html += "
  • Time to reach goal: " + Math.ceil(weeksToGoal) + " weeks (approx. " + monthsToGoal.toFixed(1) + " months)
    • "; html += "
"; if (dailyTargetCalories < 1200 && gender === "female") { html += "Note: Your daily target is below 1,200 calories. Please consult a professional as very low calorie diets require supervision."; } else if (dailyTargetCalories < 1500 && gender === "male") { html += "Note: Your daily target is below 1,500 calories. Please consult a professional as very low calorie diets require supervision."; } resultContent.innerHTML = html; resultDiv.style.display = "block"; resultDiv.scrollIntoView({ behavior: 'smooth' }); }

How to Use the Science of Calorie Deficits

Losing weight effectively is rooted in thermodynamics: energy in versus energy out. This calculator uses the Mifflin-St Jeor equation, widely considered the most accurate standard for determining Basal Metabolic Rate (BMR). By calculating your Total Daily Energy Expenditure (TDEE) and applying a specific deficit, you can predict weight loss with high accuracy.

Key Definitions

  • BMR (Basal Metabolic Rate): The number of calories your body burns at rest just to keep your organs functioning.
  • TDEE (Total Daily Energy Expenditure): The total number of calories you burn per day after accounting for exercise and daily movement.
  • Calorie Deficit: Eating fewer calories than your TDEE. A deficit of roughly 7,700 calories is required to lose 1kg of body fat.

Setting a Sustainable Goal

While it is tempting to aim for rapid weight loss, health experts generally recommend losing 0.5kg to 1kg per week. Losing weight too quickly can lead to muscle loss, nutrient deficiencies, and a higher likelihood of regaining the weight (the "yo-yo" effect).

Example Calculation:
If your maintenance calories (TDEE) are 2,500 and you want to lose 0.5kg per week, you need a daily deficit of 550 calories.
2,500 – 550 = 1,950 calories per day.

Tips for Success

  1. Prioritize Protein: Protein helps preserve lean muscle mass during a calorie deficit and keeps you feeling full longer.
  2. Track Consistently: Small bites, drinks, and oils add up. Use a tracking app to ensure you stay within your calculated target.
  3. Stay Hydrated: Sometimes the brain confuses thirst with hunger. Drinking water before meals can aid in portion control.
  4. Adjust as You Go: As you lose weight, your BMR decreases because there is less of you to "fuel." Recalculate your requirements every 5kg lost.

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