Calorie Deficit for Weight Loss Calculator
Use this calculator to estimate the daily calorie deficit and target intake needed to achieve your weight loss goals over a specified period. Remember, healthy weight loss is typically 1-2 pounds per week.
Understanding Calorie Deficit for Weight Loss
Weight loss fundamentally boils down to creating a calorie deficit. This means consistently consuming fewer calories than your body burns. The widely accepted rule of thumb is that one pound of body fat is equivalent to approximately 3,500 calories. Therefore, to lose one pound, you need to create a deficit of 3,500 calories.
Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE)
Your body burns calories even at rest to maintain basic bodily functions like breathing, circulation, and cell production. This is known as your Basal Metabolic Rate (BMR). Factors like age, gender, height, and weight influence your BMR.
Your Total Daily Energy Expenditure (TDEE) is your BMR plus the calories you burn through physical activity, including exercise and non-exercise activity thermogenesis (NEAT). Your activity level significantly impacts your TDEE.
- Sedentary: Little to no exercise.
- Lightly Active: Light exercise or sports 1-3 days per week.
- Moderately Active: Moderate exercise or sports 3-5 days per week.
- Very Active: Hard exercise or sports 6-7 days per week.
- Extra Active: Very hard exercise, a physical job, or training twice a day.
How the Calculator Works
This calculator first estimates your BMR using the Mifflin-St Jeor equation, which is considered one of the most accurate BMR formulas. It then calculates your TDEE by multiplying your BMR by an activity factor based on your selected activity level.
Next, it determines the total calorie deficit required to lose your desired amount of weight over your specified timeframe. It then divides this total deficit by the number of days in your desired period to give you a daily calorie deficit. Finally, it subtracts this daily deficit from your TDEE to provide a target daily calorie intake for weight loss.
Important Considerations for Healthy Weight Loss
- Sustainable Deficit: Aim for a moderate deficit (e.g., 500-1000 calories per day) to lose 1-2 pounds per week. Larger deficits can be difficult to sustain and may lead to nutrient deficiencies or muscle loss.
- Nutrient-Dense Foods: Focus on whole, unprocessed foods to ensure you're getting essential nutrients even with reduced calorie intake.
- Hydration: Drink plenty of water throughout the day.
- Exercise: While diet is key for weight loss, exercise helps burn additional calories, build muscle (which boosts metabolism), and improve overall health.
- Consult a Professional: This calculator provides estimates. For personalized advice, especially if you have underlying health conditions, consult a doctor or a registered dietitian.
- Listen to Your Body: Adjust your intake and activity as needed. Weight loss is not always linear.
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function calculateCalorieDeficit() {
var currentWeightLbs = parseFloat(document.getElementById("currentWeight").value);
var targetWeightLbs = parseFloat(document.getElementById("targetWeight").value);
var heightInches = parseFloat(document.getElementById("heightInches").value);
var ageYears = parseFloat(document.getElementById("ageYears").value);
var gender = document.getElementById("gender").value;
var activityLevel = document.getElementById("activityLevel").value;
var desiredPeriodWeeks = parseFloat(document.getElementById("desiredPeriodWeeks").value);
var resultDiv = document.getElementById("calorieLoseResult");
// Input validation
if (isNaN(currentWeightLbs) || isNaN(targetWeightLbs) || isNaN(heightInches) || isNaN(ageYears) || isNaN(desiredPeriodWeeks) ||
currentWeightLbs <= 0 || targetWeightLbs <= 0 || heightInches <= 0 || ageYears <= 0 || desiredPeriodWeeks = currentWeightLbs) {
resultDiv.innerHTML = "Target Weight must be less than Current Weight for weight loss.";
return;
}
// Convert to metric for BMR calculation
var currentWeightKg = currentWeightLbs * 0.453592;
var heightCm = heightInches * 2.54;
// Calculate BMR (Mifflin-St Jeor Equation)
var bmr;
if (gender === "male") {
bmr = (10 * currentWeightKg) + (6.25 * heightCm) – (5 * ageYears) + 5;
} else { // female
bmr = (10 * currentWeightKg) + (6.25 * heightCm) – (5 * ageYears) – 161;
}
// Activity Factor
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 = 1.2; // Default to sedentary
}
// Calculate TDEE
var tdee = bmr * activityFactor;
// Calculate total weight loss in pounds
var totalWeightLossLbs = currentWeightLbs – targetWeightLbs;
// Total calories to lose (3500 calories per pound of fat)
var totalCaloriesToLose = totalWeightLossLbs * 3500;
// Total days in the desired period
var totalDays = desiredPeriodWeeks * 7;
// Daily calorie deficit needed
var dailyCalorieDeficit = totalCaloriesToLose / totalDays;
// Target daily calorie intake
var targetDailyCalorieIntake = tdee – dailyCalorieDeficit;
// Display results
var resultsHtml = "
Your Calorie Deficit Plan:
";
resultsHtml += "Estimated Basal Metabolic Rate (BMR):
" + Math.round(bmr) + " calories/day";
resultsHtml += "Estimated Total Daily Energy Expenditure (TDEE):
" + Math.round(tdee) + " calories/day";
resultsHtml += "To lose
" + totalWeightLossLbs.toFixed(1) + " lbs over
" + desiredPeriodWeeks.toFixed(0) + " weeks, you need:";
resultsHtml += "A total calorie deficit of:
" + Math.round(totalCaloriesToLose) + " calories";
resultsHtml += "A daily calorie deficit of:
" + Math.round(dailyCalorieDeficit) + " calories/day";
resultsHtml += "Your target daily calorie intake should be approximately:
" + Math.round(targetDailyCalorieIntake) + " calories/day";
resultsHtml += "
(Note: A healthy and sustainable weight loss rate is typically 1-2 lbs per week.)";
resultDiv.innerHTML = resultsHtml;
}