How Much Weight Will I Lose Calculator

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Weight Loss Predictor

Estimate your potential weight loss based on your personal metrics and daily calorie intake.

Male Female
Sedentary (Little/No Exercise) Light (1-3 days/week) Moderate (3-5 days/week) Active (6-7 days/week) Very Active (Heavy Physical Job)

Your Weight Loss Forecast

Estimated Total Weight Loss: 0 lbs

Estimated New Weight: 0 lbs

Daily TDEE (Maintenance): 0 calories

Daily Calorie Deficit: 0 calories

How to Calculate Your Weight Loss

Weight loss is primarily a result of a consistent calorie deficit—consuming fewer calories than your body burns for energy. Our calculator uses the Mifflin-St Jeor Equation, widely considered the most accurate standard for estimating Basal Metabolic Rate (BMR).

The Math Behind the Loss

To lose one pound of fat, you generally need a cumulative deficit of approximately 3,500 calories. This calculator works by finding your Total Daily Energy Expenditure (TDEE) and subtracting your planned daily intake to find your daily deficit.

  • BMR: The calories your body burns at rest to maintain vital functions (breathing, circulation).
  • TDEE: Your BMR multiplied by your activity level. This is the "maintenance" number.
  • Deficit: TDEE minus Daily Calorie Intake.

Example Calculation

If your maintenance calories (TDEE) are 2,500 and you eat 2,000 calories per day, you have a 500-calorie daily deficit. Over 30 days, your total deficit is 15,000 calories. 15,000 divided by 3,500 equals approximately 4.28 lbs of weight loss.

Safe Weight Loss Rates

Health professionals typically recommend a weight loss rate of 1 to 2 pounds per week. Losing weight faster than this may lead to muscle loss or nutritional deficiencies. It is important never to drop below 1,200 calories per day for women or 1,500 calories per day for men without medical supervision.

function calculateWeightLoss() { var gender = document.getElementById("wl_gender").value; var age = parseFloat(document.getElementById("wl_age").value); var weightLbs = parseFloat(document.getElementById("wl_weight").value); var heightInches = parseFloat(document.getElementById("wl_height").value); var activity = parseFloat(document.getElementById("wl_activity").value); var dailyIntake = parseFloat(document.getElementById("wl_daily_cal").value); var duration = parseFloat(document.getElementById("wl_duration").value); if (isNaN(age) || isNaN(weightLbs) || isNaN(heightInches) || isNaN(dailyIntake) || isNaN(duration)) { alert("Please fill in all fields with valid numbers."); return; } // Convert to Metric var weightKg = weightLbs * 0.453592; var heightCm = heightInches * 2.54; // BMR Calculation (Mifflin-St Jeor) var bmr = 0; if (gender === "male") { bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) + 5; } else { bmr = (10 * weightKg) + (6.25 * heightCm) – (5 * age) – 161; } // TDEE var tdee = bmr * activity; // Deficit var dailyDeficit = tdee – dailyIntake; // Results var totalDeficit = dailyDeficit * duration; var totalWeightLoss = totalDeficit / 3500; // Ensure we don't show negative loss (weight gain) as loss if (totalWeightLoss < 0) { totalWeightLoss = 0; } var newWeight = weightLbs – totalWeightLoss; // Display results document.getElementById("wl_results").style.display = "block"; document.getElementById("res_total_loss").innerHTML = totalWeightLoss.toFixed(2); document.getElementById("res_new_weight").innerHTML = newWeight.toFixed(1); document.getElementById("res_tdee").innerHTML = Math.round(tdee); document.getElementById("res_deficit").innerHTML = Math.round(dailyDeficit); // Safety Logic var safetyNotice = ""; if (gender === "female" && dailyIntake < 1200) { safetyNotice = "Caution: It is generally not recommended for women to consume fewer than 1,200 calories per day."; } else if (gender === "male" && dailyIntake 2) { safetyNotice += " This plan results in losing more than 2 lbs per week. Consider a smaller calorie deficit for sustainable health."; } document.getElementById("wl_safety_notice").innerHTML = safetyNotice; }

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