Losing 1 pound of body fat per week is a common and sustainable goal for many individuals. This rate of weight loss is generally considered safe and achievable through a combination of dietary adjustments and increased physical activity. The key principle behind weight loss is creating a calorie deficit, meaning you consume fewer calories than your body burns.
The Math Behind Losing 1 lb Per Week
The fundamental concept is based on energy balance. Your body needs a certain amount of energy (calories) to function daily. This energy comes from the food you eat. Any excess energy is stored, primarily as fat.
Calorie Deficit: To lose weight, you must create a calorie deficit.
1 Pound of Fat: Approximately 3,500 calories are equivalent to one pound of body fat.
Weekly Goal: To lose 1 pound per week, you need to achieve a total weekly deficit of 3,500 calories.
Daily Deficit: This translates to a daily calorie deficit of 3500 calories / 7 days = 500 calories per day.
Calculator Logic Explained
This calculator helps you determine if your current habits are aligned with a 1 lb/week weight loss goal by calculating your daily calorie deficit.
Total Daily Energy Expenditure (TDEE): This is the total number of calories your body burns in a day. It includes your Basal Metabolic Rate (BMR) and calories burned through activity (exercise, daily movement, digestion). In this calculator, we simplify this by asking for your estimated Daily Calorie Expenditure.
Net Daily Calorie Intake: This is the difference between the calories you consume and the calories you burn through your metabolism and activity. It's calculated as:
Net Daily Calorie Intake = Daily Calorie Intake - Daily Calorie Expenditure
Daily Calorie Deficit: The calculator determines your actual daily calorie deficit by comparing your intake to your expenditure. A positive result indicates a deficit.
Daily Calorie Deficit = Daily Calorie Expenditure - Daily Calorie Intake
Weight Change Projection: Based on the daily deficit, we project the weekly change.
If Daily Calorie Deficit >= 500, you are on track to lose approximately 1 lb per week.
If Daily Calorie Deficit < 500 but > 0, you will lose less than 1 lb per week.
If Daily Calorie Deficit <= 0, you are not in a deficit and will not lose weight (or may gain).
How to Use the Calculator
Current Weight (lbs): Enter your current body weight in pounds.
Target Weight (lbs): Enter your desired weight in pounds. (This helps visualize the goal, though the core calculation is deficit-based).
Daily Calorie Intake (kcal): Estimate the average number of calories you consume per day from food and drinks.
Daily Calorie Expenditure (kcal): Estimate the total calories your body burns per day. This includes your Basal Metabolic Rate (BMR) plus all activity (exercise, walking, etc.). Online calculators can help estimate TDEE if you don't know this value.
Click "Calculate" to see your projected weekly weight loss and whether you are on track to meet the 1 lb/week goal.
Important Considerations:
Sustainability: A deficit of 500 calories per day is a sustainable target. Avoid extreme deficits, which can be unhealthy and lead to muscle loss.
Accuracy: Calorie expenditure estimates can vary. Listen to your body and adjust as needed.
Health Professional: Consult with a doctor or registered dietitian before making significant changes to your diet or exercise routine, especially if you have underlying health conditions.
Muscle vs. Fat: Weight loss isn't just about the number on the scale. Focusing on body composition (losing fat while preserving muscle) is crucial for long-term health.
function calculateWeightLoss() {
var currentWeight = parseFloat(document.getElementById("currentWeight").value);
var targetWeight = parseFloat(document.getElementById("targetWeight").value);
var dailyCalorieIntake = parseFloat(document.getElementById("dailyCalorieIntake").value);
var dailyCalorieExpenditure = parseFloat(document.getElementById("dailyCalorieExpenditure").value);
var resultDiv = document.getElementById("result");
resultDiv.innerHTML = "; // Clear previous results
// Input validation
if (isNaN(currentWeight) || currentWeight <= 0 ||
isNaN(targetWeight) || targetWeight <= 0 ||
isNaN(dailyCalorieIntake) || dailyCalorieIntake < 0 ||
isNaN(dailyCalorieExpenditure) || dailyCalorieExpenditure = 500) {
message = "You are on track to lose approximately 1 lb per week!";
} else if (calorieDeficitPerDay > 0 && calorieDeficitPerDay < 500) {
message = "You are in a calorie deficit, but need a larger deficit to reach 1 lb loss per week. Projected loss: " + projectedWeightLossLbs.toFixed(2) + " lbs/week.";
} else if (calorieDeficitPerDay 0) {
resultHTML += 'You need to lose approximately ' + weightDifference.toFixed(1) + ' lbs to reach your target.';
} else if (weightDifference < 0) {
resultHTML += 'Your target weight is lower than your current weight. Keep up the healthy habits!';
} else {
resultHTML += 'You are currently at your target weight!';
}
resultDiv.innerHTML = resultHTML;
}
function resetForm() {
document.getElementById("currentWeight").value = "";
document.getElementById("targetWeight").value = "";
document.getElementById("dailyCalorieIntake").value = "";
document.getElementById("dailyCalorieExpenditure").value = "";
document.getElementById("result").innerHTML = "";
}