Estimate potential weight loss and understand the impact of a 2-day fasting regimen on your body composition. This calculator is for informational purposes only.
2 Day Fasting Calculator
Enter your current body weight.
Number of days you plan to fast (typically 1-3 days for this method).
Average daily calorie deficit achieved through fasting (e.g., 500-1000 kcal). Consider your Basal Metabolic Rate (BMR) and activity level.
Your average daily calorie intake on non-fasting days or within your eating window.
Slight Adaptation (95%)
Moderate Adaptation (90%)
Significant Adaptation (85%)
Accounts for potential slowdown in metabolism during fasting. Lower values indicate greater adaptation.
Your Estimated Results
—
— Total Weight Lost (kg)
— Estimated Fat Loss (kg)
— Estimated Lean Mass Loss (kg)
Formula Used:
The calculation estimates weight loss by first determining the total calorie deficit across the fasting period. This is calculated by summing the deficit during fasting days and the deficit (or surplus) on eating days. A portion of this deficit is attributed to fat loss, and the remainder to lean mass loss, considering metabolic adaptation. A common estimate is that ~7700 kcal deficit equals 1 kg of fat loss.
Total Calorie Deficit = (Daily Calorie Deficit * Fasting Days) + ((Target Calories – Refeed Calories) * Non-Fasting Days)
Total Weight Loss (kg) = Total Calorie Deficit / 7700 (approx. kcal per kg fat) * Metabolic Adaptation Factor
Estimated Fat Loss (kg) = Total Weight Loss * (1 – (Lean Mass Loss %))
Estimated Lean Mass Loss (kg) = Total Weight Loss – Estimated Fat Loss
Weight Loss Estimation Table
Weight Loss Estimates Based on Inputs
Metric
Value
Current Weight
—
Fasting Duration
—
Daily Deficit (Fasting)
—
Daily Calories (Eating)
—
Metabolic Adaptation
—
Estimated Total Weight Lost (kg)
—
Estimated Fat Loss (kg)
—
Estimated Lean Mass Loss (kg)
—
Projected Weight Loss Over Time
Daily Weight Change Projection
What is 2 Day Fasting for Weight Loss?
The 2 day fasting for weight loss strategy, often referred to as a "2-day diet" or "fasting mimicking diet" principles applied to short durations, involves abstaining from food for approximately 48 hours, followed by a period of normal or controlled eating. This cyclical approach aims to leverage the physiological state of fasting to accelerate fat loss, potentially induce cellular repair processes (autophagy), and improve insulin sensitivity. It's distinct from prolonged fasting and requires careful planning and execution.
This method is typically suited for individuals who have some experience with intermittent fasting, are generally healthy, and have a clear weight loss goal. It's crucial that individuals consider their health status, lifestyle, and consult with a healthcare professional before embarking on such a regimen. It is not intended for pregnant or breastfeeding women, individuals with a history of eating disorders, or those with certain medical conditions like type 1 diabetes or severe hypoglycemia.
Common misconceptions about 2 day fasting for weight loss include the belief that it's a magic bullet for effortless weight loss, that one can eat excessively during the eating window without consequence, or that it leads to rapid, unsustainable muscle loss. In reality, effective implementation requires caloric awareness during eating periods, and while some lean mass loss is possible, it can be minimized with proper nutrition and resistance training.
2 Day Fasting Weight Loss Formula and Mathematical Explanation
Calculating the potential weight loss from a 2 day fasting for weight loss regimen involves estimating the total calorie deficit over a specific period. The core principle is that a consistent calorie deficit leads to weight loss, with a significant portion of this loss typically coming from fat stores.
The primary formula aims to quantify this deficit and translate it into kilograms of lost body weight. Here's a breakdown:
Step 1: Calculate Total Calorie Deficit During Fasting Days.
This assumes a baseline metabolic rate and a target deficit achieved by not eating.
Deficit_Fasting = Daily Calorie Deficit * Fasting Duration
Step 2: Calculate Calorie Balance During Eating Days.
This considers the average calories consumed versus the body's needs. If the goal is weight loss, the eating days should also contribute to a deficit.
Deficit_Eating = (Maintenance Calories – Refeed Calories) * Non-Fasting Days
(For simplicity in the calculator, we focus on the *deficit per day* during fasting and *average daily calories* during refeeding, implying a deficit is maintained.)
Step 3: Calculate Total Calorie Deficit.
Summing the deficits from both fasting and eating periods.
Total_Deficit = Deficit_Fasting + Deficit_Eating
Step 4: Convert Calorie Deficit to Weight Loss.
Approximately 7700 kilocalories (kcal) deficit is required to lose 1 kilogram of body fat. However, during significant calorie restriction, a portion of the weight loss can also come from lean body mass (muscle, water). The metabolic adaptation factor adjusts the overall efficiency of calorie expenditure.
Estimated_Weight_Loss_kg = (Total_Deficit / 7700) * Metabolic Adaptation Factor
Step 5: Estimate Fat Loss vs. Lean Mass Loss.
This is an approximation. While challenging to predict precisely, a common approach is to assume a certain percentage of weight lost is fat, and the remainder is lean mass. The calculator uses a simplified model where the "Total Weight Loss" is directly influenced by the metabolic adaptation factor, and then further breaks it down.
Estimated_Fat_Loss_kg = Estimated_Weight_Loss_kg * (1 – Lean_Mass_Loss_Proportion) Estimated_Lean_Mass_Loss_kg = Estimated_Weight_Loss_kg – Estimated_Fat_Loss_kg
(Note: The calculator simplifies this by using the adaptation factor on the total estimated deficit.)
Variables Table
Variable
Meaning
Unit
Typical Range
Current Weight
The starting weight of the individual.
Kilograms (kg)
40 – 150+ kg
Fasting Duration
Number of consecutive days food is avoided.
Days
1 – 7 days (2 days is common)
Daily Calorie Deficit (Fasting)
Estimated reduction in calories burned vs. consumed per day during fasting. Approximated by BMR/RMR.
Kilocalories (kcal)
500 – 1500 kcal
Average Daily Calories (Eating)
Average calorie intake during the non-fasting period.
Kilocalories (kcal)
1500 – 2500 kcal
Metabolic Adaptation Factor
A multiplier reflecting how efficiently the body utilizes calories during a deficit. Lower values mean greater adaptation (slower metabolism).
Unitless
0.85 – 0.98
Total Weight Loss
The estimated total reduction in body mass.
Kilograms (kg)
Dependent on inputs
Estimated Fat Loss
The estimated amount of body fat lost.
Kilograms (kg)
Dependent on inputs
Estimated Lean Mass Loss
The estimated amount of non-fat tissue (muscle, water) lost.
Kilograms (kg)
Dependent on inputs
Practical Examples (Real-World Use Cases)
Example 1: Moderate Weight Loss Goal
Sarah is 75 kg and wants to lose approximately 2 kg in a week using a 2 day fasting for weight loss approach. She plans to fast for 2 days, aiming for a daily deficit of 700 kcal while fasting. On her 5 eating days, she plans to consume around 1800 kcal, maintaining a slight deficit from her estimated maintenance of 2200 kcal. She assumes a moderate metabolic adaptation factor of 0.90.
Average Daily Calories During Eating Window: 1800 kcal
Metabolic Adaptation Factor: 0.90
Calculation:
Deficit from fasting days: 700 kcal/day * 2 days = 1400 kcal
Deficit from eating days: (2200 kcal – 1800 kcal) * 5 days = 400 kcal/day * 5 days = 2000 kcal
Total Deficit: 1400 kcal + 2000 kcal = 3400 kcal
Estimated Weight Loss (kg): (3400 kcal / 7700 kcal/kg) * 0.90 ≈ 0.44 kg * 0.90 ≈ 0.40 kg
Estimated Fat Loss (kg): Assuming ~80% fat loss during significant deficits, this is complex. The calculator focuses on total loss from deficit.
Interpretation: While the total calorie deficit is significant, the immediate weight loss from a 2-day fast is often a mix of water, glycogen, and some fat. Sarah might see a drop of around 0.40 kg directly attributable to the deficit, plus potential additional water weight fluctuations. The calculator output would reflect this estimated kilogram loss. For more substantial loss, longer fasting periods or stricter eating window control might be needed. This example highlights the importance of looking beyond just the deficit. Proper hydration and electrolyte balance are key during intermittent fasting.
Example 2: Aggressive Fat Loss Attempt
Mark weighs 90 kg and is aiming for rapid fat loss. He decides on a 2-day fast, planning a substantial deficit of 1000 kcal per fasting day. For his 5 eating days, he restricts intake to 1500 kcal, aiming for a significant deficit. He chooses a lower metabolic adaptation factor of 0.85, anticipating a stronger metabolic slowdown.
Average Daily Calories During Eating Window: 1500 kcal
Metabolic Adaptation Factor: 0.85
Calculation:
Deficit from fasting days: 1000 kcal/day * 2 days = 2000 kcal
Deficit from eating days: (Approx. 2500 kcal maintenance – 1500 kcal) * 5 days = 1000 kcal/day * 5 days = 5000 kcal
Total Deficit: 2000 kcal + 5000 kcal = 7000 kcal
Estimated Weight Loss (kg): (7000 kcal / 7700 kcal/kg) * 0.85 ≈ 0.91 kg * 0.85 ≈ 0.77 kg
Estimated Fat Loss (kg): Again, the calculator focuses on total deficit conversion.
Interpretation: Mark's aggressive approach creates a large calorie deficit. The calculator estimates around 0.77 kg of weight loss, influenced by the lower metabolic adaptation factor. It's important for Mark to be aware that such a large deficit might lead to more significant lean mass loss and potential side effects like fatigue or nutrient deficiencies if not managed carefully. He should monitor his energy levels and consider incorporating strength training to preserve muscle. This highlights the trade-offs between speed and sustainability in weight loss. Ensure adequate protein intake on eating days to support muscle preservation. This strategy should ideally be short-term and part of a broader sustainable weight management plan.
How to Use This 2 Day Fasting Weight Loss Calculator
Using the 2 day fasting for weight loss calculator is straightforward. Follow these steps to get your estimated results:
Enter Current Weight: Input your starting weight in kilograms (kg). This provides a baseline for calculations.
Specify Fasting Duration: Set the number of days you intend to fast. The calculator is pre-set to 2 days, but you can adjust it within a reasonable range.
Estimate Daily Calorie Deficit During Fasting: This is a crucial input. It represents the number of calories your body is expected to burn beyond what it consumes (which is zero during fasting). A common estimate is your Basal Metabolic Rate (BMR) or Resting Metabolic Rate (RMR). You can estimate your RMR using online calculators.
Input Average Daily Calories During Eating Window: Enter the average number of calories you plan to consume on the days you are not fasting. This should ideally be below your maintenance calories to continue contributing to a deficit.
Select Metabolic Adaptation Factor: Choose the option that best reflects your understanding of how your metabolism might react. 'Slight Adaptation' assumes your metabolism remains relatively stable, while 'Significant Adaptation' accounts for a potential slowdown. Beginners might start with a higher factor.
Click 'Calculate': Once all fields are populated, click the 'Calculate' button.
Reading Your Results:
Primary Result (Total Weight Lost): This is the main figure, showing the estimated total kilograms you might lose based on the inputs. Remember, this includes water weight, glycogen, and fat.
Estimated Fat Loss: A subset of the total weight loss, specifically targeting body fat reduction.
Estimated Lean Mass Loss: The portion of weight loss estimated to come from muscle and other non-fat tissues. Minimizing this is a key goal of healthy weight loss.
Table and Chart: These provide a detailed breakdown and visual representation of your inputs and projected outcomes.
Decision-Making Guidance:
Use these results as an estimate, not a definitive prediction. If the projected weight loss is significantly higher or lower than expected, review your input values, particularly the calorie deficit and eating window intake. Consider your individual response to fasting and adjust your plan accordingly. Always prioritize your health and consult a healthcare provider if you have concerns. For sustained results, combine fasting with balanced nutrition and regular exercise, as discussed in effective weight loss strategies.
Key Factors That Affect 2 Day Fasting Weight Loss Results
Several factors can significantly influence the effectiveness and outcome of a 2 day fasting for weight loss protocol. Understanding these can help in setting realistic expectations and optimizing your approach.
Basal Metabolic Rate (BMR) & Resting Metabolic Rate (RMR): Your individual metabolic rate is the foundation of calorie expenditure. A higher BMR means your body burns more calories at rest, potentially leading to a larger deficit and faster weight loss during fasting. Factors like age, sex, muscle mass, and genetics influence BMR.
Accuracy of Calorie Tracking: Whether estimating deficits during fasting or tracking intake during eating periods, precision is key. Overestimating your deficit or underestimating your intake will lead to less weight loss than anticipated. For 2 day fasting for weight loss, accurately estimating the deficit achieved by simply not eating is challenging but crucial.
Hydration and Electrolyte Balance: Dehydration can be mistaken for hunger and can affect metabolism. Maintaining adequate water intake is vital. During fasting, electrolyte balance (sodium, potassium, magnesium) is also critical to prevent side effects like headaches and fatigue, which could indirectly impact adherence and results. Proper intake during eating windows is also important.
Muscle Mass: Individuals with higher muscle mass tend to have a higher metabolism. While significant calorie restriction can lead to muscle loss, maintaining or even building muscle through resistance training during eating periods can help preserve metabolic rate and improve body composition, leading to better long-term results. This is a key consideration for body recomposition.
Activity Level (NEAT & Exercise): Non-Exercise Activity Thermogenesis (NEAT) – the calories burned through daily activities like walking and fidgeting – plus calories burned during structured exercise, significantly contribute to the total daily energy expenditure. Maintaining activity levels during eating periods, and appropriate activity during fasting, can enhance the calorie deficit.
Sleep Quality and Stress Levels: Poor sleep and high stress levels can negatively impact hormones like cortisol and ghrelin, potentially increasing appetite, promoting fat storage (especially abdominal fat), and increasing cravings for high-calorie foods. This can counteract the intended calorie deficit of fasting. Managing stress and prioritizing sleep are therefore essential components of successful weight management.
Nutrient Timing and Composition During Eating Window: While the calculator focuses on total calories, the macronutrient composition (protein, carbs, fats) and nutrient timing during the eating period play a role. Adequate protein intake is crucial for satiety and muscle preservation. Focusing on whole, unprocessed foods ensures better micronutrient intake.
Frequently Asked Questions (FAQ)
Q1: How much weight can I realistically lose with 2 day fasting?
A realistic estimate for weight loss over a 2-day fast is typically between 0.5 kg to 1.5 kg. This includes water weight, glycogen stores, and a smaller amount of fat. The exact amount depends heavily on your starting weight, metabolic rate, calorie intake on eating days, and hydration levels. Our calculator provides an estimate based on your inputs.
Q2: Is 2 day fasting safe for everyone?
No, 2 day fasting is not safe for everyone. It's generally not recommended for individuals who are pregnant or breastfeeding, have a history of eating disorders, have type 1 diabetes, are underweight, or have certain chronic medical conditions. Always consult with a healthcare professional before starting any fasting regimen.
Q3: What should I eat after a 2-day fast?
It's best to break your fast gently with easily digestible foods. Start with small portions of nutrient-dense options like bone broth, a small salad with lean protein, avocado, or steamed vegetables. Avoid large, heavy, or high-carbohydrate meals immediately after fasting, as this can cause digestive discomfort. Gradually reintroduce your regular meals over a few hours.
Q4: Will I lose muscle mass during a 2-day fast?
Some lean mass loss is possible with prolonged fasting, but a 2-day fast is relatively short. If you maintain adequate protein intake during your eating periods and incorporate resistance training, muscle loss can be minimized. The calculator provides an estimate for lean mass loss, but individual results vary.
Q5: Can I drink anything during the 2-day fast?
Yes, staying hydrated is crucial. You can drink plenty of water, black coffee, plain tea (herbal or green), and sparkling water without any added sweeteners or calories. These beverages can help manage hunger and support metabolic function during the fasting period.
Q6: How often can I do a 2-day fast?
The frequency depends on your individual health, goals, and how your body responds. Many people incorporate a 2-day fast once a week or once every two weeks as part of a larger weight management strategy. Listen to your body; if you feel excessively fatigued or unwell, it's likely too frequent or too intense. Consider this as part of your overall healthy lifestyle choices.
Q7: Does the 7700 kcal = 1 kg fat rule still apply during fasting?
The 7700 kcal per kg of fat is a widely used approximation, but it's not absolute. It primarily relates to stored body fat. During periods of significant calorie restriction like fasting, a larger proportion of immediate weight loss can come from water and glycogen depletion, which are not directly tied to this fat-burning conversion rate. Metabolic adaptation also plays a role in slowing down the process.
Q8: What is metabolic adaptation and why is it included?
Metabolic adaptation refers to the body's physiological response to prolonged calorie restriction, where metabolism slows down to conserve energy. Including a metabolic adaptation factor acknowledges that the body doesn't linearly burn calories during a deficit. A lower factor (e.g., 0.85) suggests a more pronounced slowdown, resulting in potentially less weight loss than a simple calorie deficit calculation would suggest. It adds a layer of realism to the estimations.
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// Simplified estimation for fat vs lean mass loss
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// Simpler approach: Assume a portion of the TOTAL estimated weight loss occurs each day.
// Let's distribute the total estimated weight loss over the observed period.
// Weight loss on fasting days contributes more significantly to immediate drop
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// Ensure weight doesn't go below zero and fat loss doesn't exceed plausible limits
if (currentDayWeight < 0) currentDayWeight = 0;
if (currentDayFatKg parseFloat(currentWeight)) currentDayFatKg = parseFloat(currentWeight);
projectedWeight.push(currentDayWeight);
estimatedFatLossSeries.push(currentDayFatKg);
}
weightLossChartInstance = new Chart(ctx, {
type: 'line',
data: {
labels: labels,
datasets: [{
label: 'Projected Total Weight (kg)',
data: projectedWeight,
borderColor: '#004a99',
backgroundColor: 'rgba(0, 74, 153, 0.1)',
fill: true,
tension: 0.3 // Slight curve
}, {
label: 'Estimated Cumulative Fat Loss (kg)',
data: estimatedFatLossSeries,
borderColor: '#28a745',
backgroundColor: 'rgba(40, 167, 69, 0.1)',
fill: true,
tension: 0.3
}]
},
options: {
responsive: true,
maintainAspectRatio: false,
scales: {
y: {
beginAtZero: false,
title: {
display: true,
text: 'Weight (kg)'
}
},
x: {
title: {
display: true,
text: 'Day'
}
}
},
plugins: {
legend: {
position: 'top',
},
title: {
display: true,
text: 'Projected Weight and Fat Loss Over 14 Days'
}
}
}
});
}
function clearChart() {
var canvas = getElement('weightLossChart');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
if (weightLossChartInstance) {
weightLossChartInstance.destroy();
weightLossChartInstance = null;
}
}
// FAQ Toggle Function
function toggleFaq(element) {
var p = element.nextElementSibling;
if (p.style.display === 'block') {
p.style.display = 'none';
} else {
p.style.display = 'block';
}
}
// Initial calculation on page load
document.addEventListener('DOMContentLoaded', function() {
calculateWeightLoss();
// Ensure canvas context is available before attempting to draw
var canvas = getElement('weightLossChart');
if (canvas && canvas.getContext) {
updateChart(
getElement('currentWeight').value,
getElement('fastingDuration').value,
getElement('deficitPerDay').value,
getElement('refeedCalories').value,
getElement('metabolicAdaptation').value,
parseFloat(getElement('currentWeight').value) * 28 // Pass estimated maintenance
);
}
});
// —– Start Pure Canvas Chart Implementation —–
// This section REPLACES the Chart.js part.
var weightLossChartInstance = null; // Keep this for potential destruction if needed, though not with pure canvas updates.
function updateChart(currentWeight, fastingDuration, deficitPerDay, refeedCalories, metabolicAdaptation, estimatedMaintenance) {
var canvas = getElement('weightLossChart');
var ctx = canvas.getContext('2d');
var chartWidth = canvas.offsetWidth;
var chartHeight = canvas.offsetHeight;
var padding = 40; // Padding around the chart area
var graphAreaWidth = chartWidth – 2 * padding;
var graphAreaHeight = chartHeight – 2 * padding;
// Clear the canvas before drawing
ctx.clearRect(0, 0, chartWidth, chartHeight);
// — Calculate Data Points —
var dataPointsCount = 14; // Project for 14 days
var labels = [];
var projectedWeightValues = [];
var estimatedFatLossValues = [];
var currentDayWeight = parseFloat(currentWeight);
var currentCumulativeFatLoss = 0;
var estimatedMaintenanceCalc = parseFloat(currentWeight) * 28; // Rough estimate
var deficitEatingDaysCalc = (estimatedMaintenanceCalc – parseFloat(refeedCalories));
if (deficitEatingDaysCalc < 0) deficitEatingDaysCalc = 0;
var totalDeficitForCycle = (parseFloat(deficitPerDay) * parseInt(fastingDuration)) + (deficitEatingDaysCalc * (7 – parseInt(fastingDuration)));
var totalWeightLossEstimate = (totalDeficitForCycle / 7700) * parseFloat(metabolicAdaptation);
var estimatedFatLossTotal = totalWeightLossEstimate * 0.75; // Approximation
var estimatedLeanMassLossTotal = totalWeightLossEstimate * 0.25; // Approximation
// Ensure estimates are not NaN or negative
totalWeightLossEstimate = isNaN(totalWeightLossEstimate) || totalWeightLossEstimate < 0 ? 0 : totalWeightLossEstimate;
estimatedFatLossTotal = isNaN(estimatedFatLossTotal) || estimatedFatLossTotal < 0 ? 0 : estimatedFatLossTotal;
estimatedLeanMassLossTotal = isNaN(estimatedLeanMassLossTotal) || estimatedLeanMassLossTotal < 0 ? 0 : estimatedLeanMassLossTotal;
var dailyWeightLossRate = totalWeightLossEstimate / dataPointsCount;
var dailyFatLossRate = estimatedFatLossTotal / dataPointsCount;
for (var i = 0; i < dataPointsCount; i++) {
labels.push('Day ' + (i + 1));
var dayLabel = i + 1;
var dayInCycle = dayLabel % 7;
if (dayInCycle === 0) dayInCycle = 7;
var weightChangeToday = 0;
if (dayInCycle <= parseInt(fastingDuration)) { // Fasting day
weightChangeToday = -dailyWeightLossRate * 1.2; // Slightly more aggressive loss on fasting days
} else { // Eating day
weightChangeToday = -dailyWeightLossRate * 0.8; // Slightly less aggressive loss on eating days
}
currentDayWeight += weightChangeToday;
currentCumulativeFatLoss += dailyFatLossRate;
// Clamp values
if (currentDayWeight < 0) currentDayWeight = 0;
if (currentCumulativeFatLoss parseFloat(currentWeight)) currentCumulativeFatLoss = parseFloat(currentWeight); // Cannot lose more fat than initial weight
projectedWeightValues.push(currentDayWeight);
estimatedFatLossValues.push(currentCumulativeFatLoss);
}
// — Find Max Values for Scaling —
var maxYWeight = parseFloat(currentWeight); // Max weight is starting weight
var minYWeight = Math.min.apply(null, projectedWeightValues);
if (minYWeight < 0) minYWeight = 0; // Weight cannot be negative
var weightRange = maxYWeight – minYWeight;
var maxFatLoss = Math.max.apply(null, estimatedFatLossValues);
var fatRange = maxFatLoss;
// Determine the dominant range for the Y-axis to scale both series appropriately
var effectiveMaxY = Math.max(maxYWeight, maxFatLoss + (maxFatLoss * 0.1)); // Add some buffer for fat loss scale
var effectiveMinY = 0;
var effectiveYRange = effectiveMaxY – effectiveMinY;
// — Drawing Functions —
function drawLine(ctx, x1, y1, x2, y2, color, lineWidth = 2) {
ctx.beginPath();
ctx.moveTo(x1, y1);
ctx.lineTo(x2, y2);
ctx.strokeStyle = color;
ctx.lineWidth = lineWidth;
ctx.stroke();
}
function drawPoint(ctx, x, y, radius, color) {
ctx.beginPath();
ctx.arc(x, y, radius, 0, 2 * Math.PI);
ctx.fillStyle = color;
ctx.fill();
}
function drawLabel(ctx, text, x, y, color, align = 'center', baseline = 'middle', size = 12) {
ctx.fillStyle = color;
ctx.textAlign = align;
ctx.textBaseline = baseline;
ctx.font = size + 'px Segoe UI, Tahoma, Geneva, Verdana, sans-serif';
ctx.fillText(text, x, y);
}
// — Draw Axes —
ctx.strokeStyle = '#ccc';
ctx.lineWidth = 1;
// Y-Axis (Weight)
var yAxisX = padding;
ctx.beginPath();
ctx.moveTo(yAxisX, padding);
ctx.lineTo(yAxisX, chartHeight – padding);
ctx.stroke();
// X-Axis (Time)
var xAxisY = chartHeight – padding;
ctx.beginPath();
ctx.moveTo(padding, xAxisY);
ctx.lineTo(chartWidth – padding, xAxisY);
ctx.stroke();
// — Draw Labels and Ticks —
var numXTicks = dataPointsCount;
var xStep = graphAreaWidth / numXTicks;
for (var i = 0; i <= numXTicks; i++) {
var x = padding + i * xStep;
drawLabel(ctx, labels[i] || '', x, xAxisY + 15, '#666');
// Draw vertical tick marks (optional, can clutter)
// drawLine(ctx, x, xAxisY, x, xAxisY + 5, '#ccc');
}
var numYTicks = 5; // Number of ticks on Y axis
for (var i = 0; i <= numYTicks; i++) {
var yValue = effectiveMaxY – (i / numYTicks) * effectiveYRange;
var y = padding + (effectiveMaxY – yValue) / effectiveYRange * graphAreaHeight;
// Draw horizontal tick marks
drawLine(ctx, padding – 5, y, padding, y, '#ccc');
// Draw Y-axis label (Weight)
var labelText = yValue.toFixed(1) + ' kg';
drawLabel(ctx, labelText, padding – 10, y, '#666', 'right', 'middle');
}
// Label for the right axis (Fat Loss) – using a second scale is complex without a library.
// We'll represent fat loss relative to the same axis, potentially requiring interpretation.
// A simpler approach for pure canvas: Overlay or adjust context.
// Let's try to plot both on the same scale for simplicity, noting the limitation.
// The second dataset represents cumulative fat loss, which starts at 0 and increases.
// We'll plot this starting from the bottom left (0,0 relative to graph area) and increasing.
// — Draw Data Series —
ctx.lineWidth = 2;
// Series 1: Projected Total Weight
ctx.strokeStyle = '#004a99';
ctx.fillStyle = 'rgba(0, 74, 153, 0.1)';
ctx.beginPath();
var startX = padding;
var startY = padding + (effectiveMaxY – projectedWeightValues[0]) / effectiveYRange * graphAreaHeight;
ctx.moveTo(startX, startY);
var pointsWeight = []; // Store points for fill
pointsWeight.push({x: startX, y: startY});
for (var i = 0; i < dataPointsCount; i++) {
var x = padding + (i + 1) * xStep;
var y = padding + (effectiveMaxY – projectedWeightValues[i]) / effectiveYRange * graphAreaHeight;
ctx.lineTo(x, y);
pointsWeight.push({x: x, y: y});
}
ctx.stroke();
// Fill area for weight
ctx.beginPath();
ctx.moveTo(pointsWeight[0].x, pointsWeight[0].y);
for(var i = 1; i < pointsWeight.length; i++) {
ctx.lineTo(pointsWeight[i].x, pointsWeight[i].y);
}
ctx.lineTo(pointsWeight[pointsWeight.length – 1].x, xAxisY); // Line to bottom axis
ctx.lineTo(pointsWeight[0].x, xAxisY); // Line to start of bottom axis
ctx.closePath();
ctx.fill();
// Series 2: Estimated Cumulative Fat Loss
ctx.strokeStyle = '#28a745';
ctx.fillStyle = 'rgba(40, 167, 69, 0.1)';
ctx.beginPath();
var startFatX = padding;
// Fat loss starts at 0 and increases. Relative to the graph area.
var startFatY = padding + (effectiveMaxY – 0) / effectiveYRange * graphAreaHeight; // Corresponds to 0 fat loss on the scale
ctx.moveTo(startFatX, startFatY);
var pointsFat = [];
pointsFat.push({x: startFatX, y: startFatY});
for (var i = 0; i < dataPointsCount; i++) {
var x = padding + (i + 1) * xStep;
// Fat loss increases, so Y value decreases on the screen scale if plotted directly against weight.
// To show it as an increasing trend, we plot cumulative fat loss.
// If we want to show it relative to the *current* weight, it's complex.
// Let's plot cumulative fat loss on the same axis, starting from 0 and increasing.
var y = padding + (effectiveMaxY – estimatedFatLossValues[i]) / effectiveYRange * graphAreaHeight;
ctx.lineTo(x, y);
pointsFat.push({x: x, y: y});
}
ctx.stroke();
// Fill area for fat loss
ctx.beginPath();
ctx.moveTo(pointsFat[0].x, pointsFat[0].y);
for(var i = 1; i < pointsFat.length; i++) {
ctx.lineTo(pointsFat[i].x, pointsFat[i].y);
}
ctx.lineTo(pointsFat[pointsFat.length – 1].x, xAxisY); // Line to bottom axis
ctx.lineTo(pointsFat[0].x, xAxisY); // Line to start of bottom axis
ctx.closePath();
ctx.fill();
// — Add Title and Legend (Simplified) —
drawLabel(ctx, 'Projected Weight Loss Over Time', chartWidth / 2, padding / 2, '#004a99', 'center', 'middle', 16);
// Simplified legend
var legendY = padding + 20;
var legendXStart = padding;
ctx.fillStyle = '#004a99';
ctx.fillRect(legendXStart, legendY, 15, 5); // Color block for weight
drawLabel(ctx, 'Projected Total Weight (kg)', legendXStart + 25, legendY + 2.5, '#333', 'left');
var legendFatY = legendY + 15;
ctx.fillStyle = '#28a745';
ctx.fillRect(legendXStart, legendFatY, 15, 5); // Color block for fat loss
drawLabel(ctx, 'Estimated Cumulative Fat Loss (kg)', legendXStart + 25, legendFatY + 2.5, '#333', 'left');
}
function clearChart() {
var canvas = getElement('weightLossChart');
var ctx = canvas.getContext('2d');
ctx.clearRect(0, 0, canvas.width, canvas.height);
}
// —– End Pure Canvas Chart Implementation —–
// Initial calculation on page load
document.addEventListener('DOMContentLoaded', function() {
calculateWeightLoss();
// Ensure canvas context is available before attempting to draw
var canvas = getElement('weightLossChart');
if (canvas && canvas.getContext) {
updateChart(
getElement('currentWeight').value,
getElement('fastingDuration').value,
getElement('deficitPerDay').value,
getElement('refeedCalories').value,
getElement('metabolicAdaptation').value,
parseFloat(getElement('currentWeight').value) * 28 // Pass estimated maintenance
);
}
});