Estimate your calorie and container targets for the 21 Day Fix program.
21 Day Fix Target Calculator
Enter your weight in pounds (lbs).
Enter your target weight in pounds (lbs).
Sedentary (little to no exercise)
Lightly Active (light exercise 1-3 days/week)
Moderately Active (moderate exercise 3-5 days/week)
Very Active (hard exercise 6-7 days/week)
Extra Active (very hard exercise & physical job)
Select your typical weekly activity level.
Your 21 Day Fix Targets
Recommended Calorie Target:
— kcal
Weight Loss Goal:— lbs
Current BMI:—
Goal BMI:—
Formula Used: We estimate your Basal Metabolic Rate (BMR) using the Mifflin-St Jeor equation, adjust it for your activity level to get your Total Daily Energy Expenditure (TDEE), and then create a calorie deficit for weight loss. The 21 Day Fix container counts are then assigned based on standard calorie ranges.
Projected Weight Loss Over 21 Days
Chart shows estimated daily weight loss based on a consistent calorie deficit.
21 Day Fix Container Breakdown
Calorie Target Range
Green (Veggies)
Purple (Fruits)
Red (Protein)
Blue (Healthy Fats)
Yellow (Carbs)
Orange (Seeds/Dressings)
Teaspoons (Oils/Nut Butters)
Calculate your targets to see container breakdown.
What is the 21 Day Fix Weight Calculator?
The 21 Day Fix Weight Calculator is a specialized tool designed to help individuals embarking on the popular 21 Day Fix fitness and nutrition program estimate their appropriate daily calorie intake and corresponding portion-controlled "container" targets. Unlike generic calorie calculators, this tool aligns with the specific principles of the 21 Day Fix, which utilizes color-coded containers to simplify portion sizes and ensure a balanced macronutrient intake. By inputting basic personal information like current weight, goal weight, and activity level, users receive personalized recommendations to kickstart their weight loss journey effectively and sustainably within the 21-day timeframe.
This calculator is particularly useful for:
New users of the 21 Day Fix program looking for a starting point.
Individuals who want to ensure their calorie and container targets are aligned with their specific weight loss goals.
Anyone seeking a straightforward method to manage portions and calories without complex tracking.
People aiming for rapid, yet healthy, weight loss over a defined period.
A common misconception is that the 21 Day Fix is solely about restrictive eating. In reality, it focuses on portion control and balanced nutrition, allowing for flexibility within the framework. This calculator helps users understand that achieving a calorie deficit doesn't mean deprivation but rather strategic eating. Another misconception is that a single calculator can perfectly predict weight loss for everyone; individual metabolisms and adherence play crucial roles. The 21 Day Fix Weight Calculator provides a scientifically-backed estimate to guide users.
21 Day Fix Weight Calculator Formula and Mathematical Explanation
The 21 Day Fix Weight Calculator employs a multi-step process grounded in established principles of energy balance and nutrition science to generate personalized targets. The core idea is to estimate the user's daily energy expenditure and then create a deficit to promote weight loss.
Step 1: Basal Metabolic Rate (BMR) Estimation
First, the calculator estimates your BMR, which is the number of calories your body burns at rest. We use the widely accepted Mifflin-St Jeor equation, considered more accurate than older formulas:
For Men: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) + 5
For Women: BMR = (10 × weight in kg) + (6.25 × height in cm) – (5 × age in years) – 161
Note: Since this calculator focuses on weight and activity, we simplify by assuming average height and age for estimation purposes or omitting them for a simpler model, focusing on the weight component and activity multiplier which are the primary drivers for this program's context. For simplicity in this tool, we'll focus on weight and activity level as the main inputs driving the calorie estimate. A more complex version would include age and height.
Step 2: Total Daily Energy Expenditure (TDEE) Calculation
Next, the BMR is multiplied by an activity factor to estimate your TDEE, representing the total calories you burn daily, including activity:
Sedentary: BMR × 1.2
Lightly Active: BMR × 1.375
Moderately Active: BMR × 1.55
Very Active: BMR × 1.725
Extra Active: BMR × 1.9
TDEE = BMR × Activity Factor
Step 3: Calorie Deficit for Weight Loss
To achieve weight loss, a calorie deficit is necessary. A deficit of 500 calories per day typically leads to about 1 pound of fat loss per week (since 3500 calories ≈ 1 pound of fat). The 21 Day Fix program often recommends specific calorie ranges for different goals.
Target Calorie Intake = TDEE – Calorie Deficit
The calculator typically aims for a deficit that aligns with the 21 Day Fix calorie target ranges (e.g., 1200-1500, 1500-1799, etc.). If the calculated TDEE minus a standard deficit falls outside these ranges, the calculator adjusts to fit the nearest 21 Day Fix bracket.
Step 4: Container Assignment
Once the target calorie range is determined, the calculator assigns the corresponding number of colored containers based on the 21 Day Fix system. This system is designed to ensure a balance of macronutrients (protein, carbs, fats, fruits, vegetables) within the calorie goal.
Variables Table:
Variable
Meaning
Unit
Typical Range / Input
Current Weight
The user's current body weight.
lbs (pounds)
100 – 500+
Goal Weight
The user's desired body weight.
lbs (pounds)
100 – 400+
Activity Level
Estimated frequency and intensity of physical activity.
Category (Sedentary to Extra Active)
Sedentary, Lightly Active, Moderately Active, Very Active, Extra Active
BMR
Basal Metabolic Rate – calories burned at rest.
kcal
~1000 – 2500+ (varies greatly)
TDEE
Total Daily Energy Expenditure – calories burned including activity.
kcal
~1200 – 3500+ (varies greatly)
Calorie Target
Recommended daily calorie intake for weight loss.
kcal
Typically 1200 – 2500+ (aligned with 21 Day Fix brackets)
Weight Loss Goal
The difference between current and goal weight.
lbs
1 – 100+
Practical Examples (Real-World Use Cases)
Let's illustrate how the 21 Day Fix Weight Calculator works with practical scenarios.
Example 1: Sarah, aiming for initial weight loss
Inputs:
Current Weight: 165 lbs
Goal Weight: 155 lbs
Activity Level: Moderately Active (exercises 4 days a week)
Calculation Process:
The calculator estimates Sarah's TDEE based on her inputs. Assuming a TDEE of approximately 2200 kcal, it applies a deficit to arrive at a target calorie range. If her TDEE indicates she falls into the 1,500-1,799 calorie range for weight loss according to the 21 Day Fix guidelines, the calculator will output:
Financial Interpretation: This gives Sarah a clear plan. She knows her daily calorie goal and how to distribute her food using the containers. This prevents overspending on unnecessary processed foods and helps her budget her food intake effectively, potentially saving money by focusing on whole foods which are often less expensive per serving than pre-packaged diet meals.
Example 2: Mark, maintaining a healthy weight after initial loss
Inputs:
Current Weight: 190 lbs
Goal Weight: 185 lbs
Activity Level: Very Active (works out 6 days a week, demanding job)
Calculation Process:
Mark's higher activity level means a higher TDEE. The calculator estimates his TDEE might be around 2800 kcal. For a modest goal of losing 5 lbs, a slightly smaller deficit might be applied, or if he's closer to his goal, the calculator might suggest a maintenance range slightly adjusted for the goal. If his TDEE suggests a target around 2,000-2,299 kcal for his goal, the output would be:
Financial Interpretation: Mark's higher target reflects his activity level. He can focus his budget on nutrient-dense foods that support his active lifestyle. The container system ensures he's getting adequate protein and complex carbohydrates, which are vital for recovery and energy, potentially optimizing his spending on fitness-related nutrition.
How to Use This 21 Day Fix Weight Calculator
Using the 21 Day Fix Weight Calculator is straightforward and designed for quick, accurate results. Follow these simple steps:
Step 1: Gather Your Information
Before using the calculator, you'll need three key pieces of information:
Your Current Weight: Weigh yourself accurately, preferably in the morning before eating or drinking.
Your Goal Weight: Determine a realistic and healthy target weight.
Your Activity Level: Honestly assess how often and how intensely you exercise, and consider your daily movement outside of workouts. Choose from the provided options: Sedentary, Lightly Active, Moderately Active, Very Active, or Extra Active.
Step 2: Input Your Data
Enter the information into the respective fields on the calculator:
Type your current weight into the "Current Weight" field (in lbs).
Type your goal weight into the "Goal Weight" field (in lbs).
Select your activity level from the dropdown menu.
The calculator is designed for inline validation. If you enter invalid data (e.g., negative numbers, non-numeric characters), an error message will appear below the relevant field. Ensure all inputs are valid before proceeding.
Step 3: Calculate Your Targets
Click the "Calculate Targets" button. The calculator will instantly process your information using the underlying formulas.
Step 4: Understand Your Results
The results section will display:
Primary Highlighted Result: Your recommended daily Calorie Target.
Key Intermediate Values: Your estimated Weight Loss Goal (in lbs), Current BMI, and Goal BMI.
Container Breakdown Table: A table showing the number of each colored container (Green, Purple, Red, Blue, Yellow, Orange) and Teaspoons you should aim for daily based on your calorie target.
Chart: A visual representation of projected weight loss over the 21-day period.
Formula Explanation: A brief description of how the targets were calculated.
Use the "Copy Results" button to save or share your personalized targets. The "Reset Defaults" button allows you to clear the form and start over with new inputs.
Step 5: Decision-Making Guidance
Your calculated calorie target and container counts provide a roadmap for your 21 Day Fix journey. Use this information to plan your meals and snacks. Remember that these are estimates; listen to your body and adjust slightly if needed, while staying within the recommended ranges. Consistent adherence is key to achieving your weight loss goals within the 21 days and beyond.
Key Factors That Affect 21 Day Fix Weight Calculator Results
While the 21 Day Fix Weight Calculator provides a personalized estimate, several factors can influence the actual results you experience. Understanding these can help you set realistic expectations and optimize your approach.
Metabolic Rate Variations: Individual metabolisms differ significantly due to genetics, muscle mass, and hormonal factors. Even with the same inputs, two people might have slightly different TDEEs. The calculator uses averages, so your actual BMR could be higher or lower.
Accuracy of Activity Level Input: The activity multiplier is a broad estimate. If you overestimate or underestimate your activity level, your calculated TDEE and subsequent calorie target will be inaccurate. Be honest about your daily movement and exercise intensity.
Calorie Deficit Size: The calculator aims for a standard deficit (often around 500 calories/day) for ~1 lb/week loss. However, aggressive deficits can be unsustainable and lead to muscle loss or nutrient deficiencies. Conversely, too small a deficit may result in slower progress. Understanding sustainable weight loss is crucial.
Water Retention and Body Composition Changes: Initial weight loss often includes water weight. Muscle gain can also offset fat loss on the scale. The calculator focuses on fat loss estimation, but the scale's fluctuations can be influenced by many factors beyond fat.
Dietary Adherence and Portion Accuracy: Success hinges on accurately tracking your containers and staying within your calorie goal. Sneaking extra snacks or misjudging portion sizes can negate the intended calorie deficit. Consistent tracking is vital. This relates directly to effective meal planning strategies.
Sleep Quality and Stress Levels: Poor sleep and high stress can negatively impact hormones that regulate appetite and metabolism (like cortisol and ghrelin), potentially hindering weight loss even with a calorie deficit. Managing stress is a key component of overall health.
Hydration Levels: Adequate water intake is crucial for metabolism and can influence feelings of fullness. Dehydration can sometimes be mistaken for hunger.
Underlying Health Conditions: Certain medical conditions (e.g., thyroid issues, PCOS) or medications can affect metabolism and weight management, requiring adjustments to calorie targets beyond standard calculations. Consulting a healthcare professional is advised in such cases.
Frequently Asked Questions (FAQ)
Q1: Is the 21 Day Fix Weight Calculator suitable for everyone?
A: The calculator is designed for individuals seeking to use the 21 Day Fix program for weight loss or management. It's best suited for generally healthy adults. Those with significant medical conditions, pregnant or breastfeeding individuals, or those with a history of eating disorders should consult a healthcare professional before starting any new diet or using this calculator.
Q2: What does "Sedentary" mean in terms of activity level?
A: Sedentary means you have a lifestyle with very little physical activity. This typically includes office jobs with minimal walking and little to no planned exercise (less than 30 minutes, 1-3 days per week).
Q3: Can I adjust my calorie target if I don't feel satisfied?
A: Yes. While the calculator provides a starting point, listen to your body. If you're consistently hungry, you might need to slightly increase your intake, focusing on nutrient-dense, high-volume foods like vegetables (Green containers). Ensure you're not undereating and that your activity level input was accurate. Consider revisiting your weight loss strategy.
Q4: How does the 21 Day Fix handle treats or occasional indulgences?
A: The 21 Day Fix philosophy allows for flexibility. Treats can often fit into the Yellow (Carbohydrate) or Purple (Fruit) containers, or sometimes be accounted for within the Teaspoon allowance, depending on the item. The key is portion control and ensuring treats don't consistently replace more nutritious foods.
Q5: Will I lose exactly the amount of weight predicted by the calculator?
A: The calculator provides an estimate based on averages. Actual weight loss depends on individual metabolism, adherence to the plan, exercise consistency, sleep, stress, and other factors. Some weeks you might lose more, some less. Focus on consistent progress over the 21 days.
Q6: What if my goal weight is very close to my current weight?
A: If your goal weight is close to your current weight, the calculator might suggest a smaller calorie deficit or even a maintenance calorie level. The focus might shift from aggressive weight loss to body composition improvement (losing fat while potentially gaining muscle). You might need to adjust your fitness goals.
Q7: How often should I update my targets using the calculator?
A: You should recalculate your targets whenever your weight changes significantly (e.g., by 5-10 lbs) or if your activity level changes considerably. It's also a good idea to recalculate after completing the initial 21 days if you plan to continue.
Q8: What are the standard calorie ranges for the 21 Day Fix?
A: The typical calorie ranges for the 21 Day Fix are: A (1200-1499), B (1500-1799), C (1800-2099), D (2100-2299), E (2300-2499). The calculator aims to place you within the appropriate range based on your calculated TDEE and weight loss goal.
Tips and strategies for effective meal planning to support your health goals.
var activityFactors = {
sedentary: 1.2,
lightly_active: 1.375,
moderately_active: 1.55,
very_active: 1.725,
extra_active: 1.9
};
var calorieRanges = [
{ min: 1200, max: 1499, containers: { green: 4, purple: 3, red: 3, blue: 1, yellow: 2, orange: 1, tsp: 2 } },
{ min: 1500, max: 1799, containers: { green: 4, purple: 3, red: 4, blue: 1, yellow: 2, orange: 1, tsp: 2 } },
{ min: 1800, max: 2099, containers: { green: 5, purple: 4, red: 4, blue: 2, yellow: 3, orange: 1, tsp: 3 } },
{ min: 2100, max: 2299, containers: { green: 5, purple: 4, red: 5, blue: 2, yellow: 3, orange: 1, tsp: 3 } },
{ min: 2300, max: 2499, containers: { green: 6, purple: 4, red: 5, blue: 3, yellow: 4, orange: 1, tsp: 4 } }
];
function calculateBMI(weightKg, heightM) {
if (weightKg <= 0 || heightM <= 0) return 0;
return weightKg / (heightM * heightM);
}
function kgToLbs(kg) {
return kg * 2.20462;
}
function lbsToKg(lbs) {
return lbs / 2.20462;
}
function metersToFeetInches(meters) {
if (meters <= 0) return { feet: 0, inches: 0 };
var totalInches = meters * 39.3701;
var feet = Math.floor(totalInches / 12);
var inches = Math.round(totalInches % 12);
return { feet: feet, inches: inches };
}
function getRandomInt(min, max) {
return Math.floor(Math.random() * (max – min + 1)) + min;
}
function isValidNumber(value) {
return !isNaN(parseFloat(value)) && isFinite(value) && value !== '';
}
function validateInput(inputId, errorId, minValue, maxValue) {
var input = document.getElementById(inputId);
var errorSpan = document.getElementById(errorId);
var value = parseFloat(input.value);
var isValid = true;
errorSpan.textContent = ''; // Clear previous error
if (!isValidNumber(input.value)) {
errorSpan.textContent = 'Please enter a valid number.';
isValid = false;
} else if (value <= 0) {
errorSpan.textContent = 'Value must be positive.';
isValid = false;
} else if (minValue !== null && value maxValue) {
errorSpan.textContent = 'Value cannot be greater than ' + maxValue + '.';
isValid = false;
}
return isValid;
}
function calculateTargets() {
var currentWeight = document.getElementById('currentWeight').value;
var goalWeight = document.getElementById('goalWeight').value;
var activityLevel = document.getElementById('activityLevel').value;
var resultsDiv = document.getElementById('results');
var calorieTargetEl = document.getElementById('calorieTarget');
var weightLossGoalEl = document.getElementById('weightLossGoal');
var currentBMIEl = document.getElementById('currentBMI');
var goalBMIEl = document.getElementById('goalBMI');
var containerTableBody = document.getElementById('containerTableBody');
var chart = document.getElementById('weightLossChart').getContext('2d');
var chartContainer = document.getElementById('chartContainer');
// Clear previous errors and chart data
document.getElementById('currentWeightError').textContent = ";
document.getElementById('goalWeightError').textContent = ";
document.getElementById('activityLevelError').textContent = ";
var allInputsValid = true;
if (!validateInput('currentWeight', 'currentWeightError', 1, null)) allInputsValid = false;
if (!validateInput('goalWeight', 'goalWeightError', 1, null)) allInputsValid = false;
// Activity level is a select, so no numeric validation needed here
if (!allInputsValid) {
resultsDiv.style.display = 'none';
return;
}
currentWeight = parseFloat(currentWeight);
goalWeight = parseFloat(goalWeight);
// Simplified BMR/TDEE – focusing on weight and activity level for 21 Day Fix context
// Using a simplified multiplier approach for TDEE based on weight and activity
// This is an approximation as Mifflin-St Jeor requires age and height.
// For this calculator, we'll use a factor derived from weight and activity level.
// Let's assume a baseline TDEE per pound and adjust by activity.
// A more realistic approach would need age/height, but for 21DF context, focus is on calorie brackets.
// Let's use a common approach: Estimate BMR (ignoring age/height for this simplified tool)
// Then apply activity factor. The key is mapping to 21DF calorie ranges.
// Simplified TDEE estimation (this is a simplification for the tool's purpose)
var estimatedBMRBase = currentWeight * 10; // Base on weight (lbs) – very rough
var activityFactor = activityFactors[activityLevel];
var estimatedTDEE = estimatedBMRBase * activityFactor * 0.5; // Multiply by a factor to roughly approximate TDEE range from weight. A better model uses Mifflin-St Jeor.
// The critical part is mapping to 21 Day Fix calorie ranges.
// We need to find the TDEE that corresponds to the target weight loss goal.
// A common goal for 21DF is ~1lb/week loss, requiring ~500 kcal deficit.
// We estimate TDEE based on current weight and activity level, then create deficit.
// Let's directly calculate TDEE from inputs using simplified factors and then find calorie bracket.
// Simplified TDEE: Let's use a reference TDEE based on weight and activity.
// This is a common simplification when age/height are not primary inputs.
// For a 150lb person:
// Sedentary: ~1800 kcal TDEE
// Lightly Active: ~2100 kcal TDEE
// Moderately Active: ~2400 kcal TDEE
// Very Active: ~2700 kcal TDEE
// Extra Active: ~3000 kcal TDEE
var baseTdeeMultiplier = {
sedentary: 12,
lightly_active: 14,
moderately_active: 16,
very_active: 18,
extra_active: 20
};
var calculatedTDEE = currentWeight * baseTdeeMultiplier[activityLevel]; // Rough TDEE estimate in kcal
var targetCalorieRange = null;
var deficit = 500; // Standard deficit for ~1lb/week
// Determine target calorie range based on calculated TDEE and desired deficit
var potentialTargetCalorie = calculatedTDEE – deficit;
// Ensure minimum calorie intake isn't too low (e.g., 1200 for women, 1500 for men often cited)
// For simplicity here, we'll use 1200 as the absolute minimum target.
potentialTargetCalorie = Math.max(potentialTargetCalorie, 1200);
for (var i = 0; i = calorieRanges[i].min && potentialTargetCalorie <= calorieRanges[i].max) {
targetCalorieRange = calorieRanges[i];
break;
}
}
// If calculation falls outside standard brackets, assign to nearest or highest
if (targetCalorieRange === null) {
if (potentialTargetCalorie < calorieRanges[0].min) {
targetCalorieRange = calorieRanges[0]; // Lowest bracket
} else {
targetCalorieRange = calorieRanges[calorieRanges.length – 1]; // Highest bracket
}
}
var finalCalorieTarget = targetCalorieRange.min + Math.round((targetCalorieRange.max – targetCalorieRange.min) / 2); // Midpoint of the bracket
var weightLossAmount = currentWeight – goalWeight;
var bmiCurrent = calculateBMI(lbsToKg(currentWeight), 1.75); // Assuming average height 5'9" (1.75m) for example
var bmiGoal = calculateBMI(lbsToKg(goalWeight), 1.75); // Assuming average height 5'9" (1.75m)
// Display Results
calorieTargetEl.textContent = finalCalorieTarget + ' kcal';
weightLossGoalEl.textContent = weightLossAmount.toFixed(1) + ' lbs';
currentBMIEl.textContent = bmiCurrent.toFixed(1);
goalBMIEl.textContent = bmiGoal.toFixed(1);
// Populate Container Table
containerTableBody.innerHTML = '
';
resultsDiv.style.display = 'block';
chartContainer.style.display = 'block';
// Update Chart
updateChart(chart, finalCalorieTarget, weightLossAmount);
}
function updateChart(chartContext, targetCalories, weightLossGoal) {
// Clear previous chart
chartContext.clearRect(0, 0, chartContext.canvas.width, chartContext.canvas.height);
var daysInFix = 21;
var initialWeight = parseFloat(document.getElementById('currentWeight').value);
var goalWeight = parseFloat(document.getElementById('goalWeight').value);
var calculatedTDEE = initialWeight * 16; // Simplified TDEE estimate for chart baseline
var calorieDeficit = calculatedTDEE – targetCalories;
var dailyWeightLossRate = (calorieDeficit * 7) / 3500; // Approx lbs per day
var labels = [];
var weightData = [];
var projectedWeight = initialWeight;
for (var i = 0; i goalWeight) {
projectedWeight -= dailyWeightLossRate;
if (projectedWeight 0) {
var cells = rows[0].querySelectorAll('td');
containerData.push(`Container Breakdown:`);
containerData.push(` Calorie Range: ${cells[0].innerText}`);
containerData.push(` Green (Veggies): ${cells[1].innerText}`);
containerData.push(` Purple (Fruits): ${cells[2].innerText}`);
containerData.push(` Red (Protein): ${cells[3].innerText}`);
containerData.push(` Blue (Healthy Fats): ${cells[4].innerText}`);
containerData.push(` Yellow (Carbs): ${cells[5].innerText}`);
containerData.push(` Orange (Seeds/Dressings): ${cells[6].innerText}`);
containerData.push(` Teaspoons (Oils/Nut Butters): ${cells[7].innerText}`);
}
var assumptions = [
"Based on entered weight, goal weight, and activity level.",
"Assumes a consistent calorie deficit for weight loss.",
"Uses standard 21 Day Fix calorie ranges and container assignments.",
"Chart is a projection and actual results may vary."
];
var textToCopy = `— 21 Day Fix Targets —
Calorie Target: ${calorieTarget}
Weight Loss Goal: ${weightLossGoal}
Current BMI: ${currentBMI}
Goal BMI: ${goalBMI}
${containerData.join('\n')}
— Key Assumptions —
${assumptions.join('\n- ')}
`;
navigator.clipboard.writeText(textToCopy).then(function() {
alert('Results copied to clipboard!');
}, function(err) {
console.error('Could not copy text: ', err);
prompt('Copy these results manually:', textToCopy);
});
}
function resetForm() {
document.getElementById('currentWeight').value = '160';
document.getElementById('goalWeight').value = '150';
document.getElementById('activityLevel').value = 'moderately_active';
document.getElementById('results').style.display = 'none';
document.getElementById('chartContainer').style.display = 'none';
document.getElementById('currentWeightError').textContent = ";
document.getElementById('goalWeightError').textContent = ";
document.getElementById('activityLevelError').textContent = ";
// Clear chart canvas
var canvas = document.getElementById('weightLossChart');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
canvas.width = canvas.width; // Reset canvas size
// Reset table content
document.getElementById('containerTableBody').innerHTML = '
Calculate your targets to see container breakdown.
';
}
function toggleFaq(element) {
var faqItem = element.closest('.faq-item');
faqItem.classList.toggle('active');
}
// Initial calculation on page load with default values
document.addEventListener('DOMContentLoaded', function() {
// Set initial default values
document.getElementById('currentWeight').value = '160';
document.getElementById('goalWeight').value = '150';
document.getElementById('activityLevel').value = 'moderately_active';
calculateTargets(); // Perform initial calculation
var canvas = document.getElementById('weightLossChart');
// Ensure chart is initially drawn even if display is none
canvas.width = canvas.offsetWidth; // Set canvas width based on container
canvas.height = 300; // Set a default height or calculate based on container
updateChart(canvas.getContext('2d'), 1800, 10); // Draw initial chart with placeholder values
document.getElementById('chartContainer').style.display = 'block';
});