Professional Projection Tool for Gastric Bypass, Sleeve, & Switch
Weight Loss Projection
Estimate your weight loss timeline based on clinical expected weight loss (EWL) curves.
Female
Male
Used to calculate Ideal Body Weight (IBW).
4 ft
5 ft
6 ft
7 ft
0 in
1 in
2 in
3 in
4 in
5 in
6 in
7 in
8 in
9 in
10 in
11 in
Your weight on the day of surgery.
Please enter a valid weight (100-1000 lbs).
Gastric Bypass (Roux-en-Y)
Gastric Sleeve (VSG)
Duodenal Switch
Lap Band
Affects the percentage of excess weight loss expected.
Projected Weight at 12 Months
0 lbs
Ideal Body Weight (IBW)0 lbs
Excess Weight (Current – IBW)0 lbs
Total Expected Loss (18 Mo)0 lbs
Formula Note: Calculation uses the Devine Formula for IBW and standard clinical Excess Weight Loss (EWL) curves: Month 1 (15%), Month 3 (30%), Month 6 (55%), Month 12 (80%), Month 18 (100% of potential).
Timeline
Projected Weight
Total Loss
EWL %
Detailed Guide: Bariatric Weight Loss Calculator by Month
Understanding your post-surgical journey is critical for long-term success. This bariatric weight loss calculator by month is designed to provide patients with a realistic, clinically-based projection of their weight loss trajectory following major bariatric procedures. Whether you are considering the Gastric Sleeve, Gastric Bypass, or Duodenal Switch, knowing the numbers helps set achievable goals.
What is a Bariatric Weight Loss Calculator by Month?
A bariatric weight loss calculator by month is a specialized tool that estimates how much weight a patient will lose at specific intervals after surgery (e.g., 1 month, 3 months, 6 months, and 1 year). Unlike generic BMI calculators, this tool focuses on "Excess Weight Loss" (EWL), which is the industry standard for measuring bariatric success.
This tool is essential for:
Pre-op Patients: To visualize the potential outcome of different surgery types.
Post-op Patients: To track progress against statistical averages.
Medical Professionals: To explain realistic expectations to candidates.
Common Misconception: Many patients believe they will reach their "Ideal Body Weight" (IBW) automatically. However, most surgeries aim to remove 60-80% of excess weight, meaning some residual weight above the IBW is normal and expected.
Bariatric Weight Loss Calculator by Month: The Formula
The calculations performed by this tool rely on two primary components: The Ideal Body Weight (IBW) calculation and the Excess Weight Loss (EWL) curve.
1. Calculating Ideal Body Weight (IBW)
We use the Devine Formula, a standard in medical pharmacology and bariatric medicine:
Men: 50 kg + 2.3 kg per inch over 5 feet.
Women: 45.5 kg + 2.3 kg per inch over 5 feet.
2. Calculating Excess Weight
Once IBW is known, we determine your Excess Weight:
Excess Weight = Current Weight – Ideal Body Weight
3. Variable Reference Table
Variable
Meaning
Typical Value
Current Weight
Weight on surgery day
200 – 600 lbs
IBW
Medically "ideal" weight
110 – 180 lbs
EWL %
% of excess weight lost
60% – 80% (Total)
Timeline
Months post-op
1 – 18 months
Practical Examples of Weight Loss Projections
To help you understand how the bariatric weight loss calculator by month works, here are two real-world scenarios.
Key Factors That Affect Bariatric Weight Loss Results
While our bariatric weight loss calculator by month uses clinical averages, individual results vary based on several factors:
Adherence to Diet: The "pouch" limits food intake, but consuming high-calorie liquids can sabotage weight loss (grazing).
Exercise Frequency: Resistance training preserves muscle mass, keeping metabolism high as weight drops.
Metabolic Adaptation: The body naturally fights weight loss by lowering metabolic rate; bariatric surgery mitigates this but does not eliminate it.
Starting BMI: Patients with higher initial BMIs often lose more total pounds but may have a lower percentage of EWL compared to lighter patients.
Age and Gender: Younger patients and men typically lose weight slightly faster due to higher muscle mass and metabolic rates.
Follow-up Care: Regular appointments with dietitians and support groups significantly improve long-term stats.
Frequently Asked Questions (FAQ)
How accurate is this bariatric weight loss calculator by month?
It is based on statistical averages (mean results). Most patients fall within +/- 15% of these projections if they follow their prescribed protocol.
Why does weight loss slow down after 6 months?
During the "honeymoon phase" (0-6 months), hormonal changes and drastic calorie restriction cause rapid loss. As the body adapts and the pouch relaxes slightly, weight loss naturally decelerates.
What if I am not losing as much as the calculator predicts?
Stalls are common, especially around week 3 and month 3. Consult your bariatric team to review your protein and water intake.
Does this calculator work for revision surgery?
Revisions (e.g., Band to Bypass) typically result in slower weight loss than primary surgeries. This calculator assumes a primary procedure.
What is "Excess Weight"?
Excess weight is the difference between your current weight and the weight considered "ideal" for your height (BMI ~25).
Which surgery loses the most weight?
Statistically, the Duodenal Switch results in the highest average EWL (80%), followed by Gastric Bypass (70%), Sleeve (60%), and Lap Band (50%).
Can I lose 100% of my excess weight?
It is possible, but statistically, most patients retain about 20-30% of their excess weight. This is still considered a highly successful clinical outcome.
How often should I weigh myself?
While this is a bariatric weight loss calculator by month, we recommend weighing weekly rather than daily to avoid anxiety over natural fluid fluctuations.
// Global chart variable
var weightChart = null;
// Initialization
window.onload = function() {
calculateResults();
};
function calculateResults() {
// 1. Get Inputs
var gender = document.getElementById('gender').value;
var heightFt = parseInt(document.getElementById('heightFt').value);
var heightIn = parseInt(document.getElementById('heightIn').value);
var currentWeight = parseFloat(document.getElementById('currentWeight').value);
var surgeryType = document.getElementById('surgeryType').value;
var weightError = document.getElementById('weightError');
// Validation
if (isNaN(currentWeight) || currentWeight 1000) {
weightError.style.display = 'block';
return;
} else {
weightError.style.display = 'none';
}
// 2. Constants & Logic
// Height in inches
var totalInches = (heightFt * 12) + heightIn;
// Calculate IBW (Devine Formula)
// Male: 50kg + 2.3kg * (inches – 60)
// Female: 45.5kg + 2.3kg * (inches – 60)
// 1 kg = 2.20462 lbs
var baseIBWKg = (gender === 'male') ? 50 : 45.5;
var heightFactor = (totalInches > 60) ? (totalInches – 60) : 0;
var ibwKg = baseIBWKg + (2.3 * heightFactor);
var ibwLbs = ibwKg * 2.20462;
// Ensure IBW isn't higher than current weight (edge case)
if (ibwLbs > currentWeight) ibwLbs = currentWeight;
// Excess Weight
var excessWeight = currentWeight – ibwLbs;
// Surgery Success Rates (Total Expected % of Excess Weight Loss)
var surgeryEfficiency = 0.60; // Default Sleeve
if (surgeryType === 'bypass') surgeryEfficiency = 0.70;
if (surgeryType === 'switch') surgeryEfficiency = 0.80;
if (surgeryType === 'band') surgeryEfficiency = 0.50;
var totalExpectedLoss = excessWeight * surgeryEfficiency;
// Loss Curve (Percentage of Total Expected Loss achieved by Month X)
// Curves approximate clinical averages
// Month: 0, 1, 3, 6, 9, 12, 18, 24
var timePoints = [0, 1, 3, 6, 9, 12, 18, 24];
var progressCurve = [0, 0.15, 0.35, 0.55, 0.70, 0.80, 1.0, 1.0]; // 100% of expected loss by month 18
var projectionData = [];
var labels = [];
var dataPoints = [];
var lossPoints = [];
for (var i = 0; i < timePoints.length; i++) {
var month = timePoints[i];
var percentComplete = progressCurve[i];
var lossToDate = totalExpectedLoss * percentComplete;
var currentProjWeight = currentWeight – lossToDate;
projectionData.push({
month: month,
weight: Math.round(currentProjWeight),
loss: Math.round(lossToDate),
ewlPct: Math.round((lossToDate / excessWeight) * 100)
});
labels.push("Mo " + month);
dataPoints.push(Math.round(currentProjWeight));
lossPoints.push(Math.round(lossToDate));
}
// 3. Update DOM
document.getElementById('ibwResult').innerText = Math.round(ibwLbs) + " lbs";
document.getElementById('excessWeightResult').innerText = Math.round(excessWeight) + " lbs";
document.getElementById('totalLossResult').innerText = Math.round(totalExpectedLoss) + " lbs";
// Specific Month 12 update
var res12 = projectionData.find(function(d) { return d.month === 12; });
document.getElementById('result12Month').innerText = res12.weight + " lbs";
// Update Table
var tableBody = document.getElementById('projectionTableBody');
tableBody.innerHTML = '';
for (var j = 0; j < projectionData.length; j++) {
if (projectionData[j].month === 0) continue; // Skip month 0 in table
var row = "
" +
"
Month " + projectionData[j].month + "
" +
"
" + projectionData[j].weight + " lbs
" +
"
-" + projectionData[j].loss + " lbs
" +
"
" + projectionData[j].ewlPct + "%
" +
"
";
tableBody.innerHTML += row;
}
// 4. Update Chart (Canvas)
drawChart(labels, dataPoints, lossPoints);
}
function drawChart(labels, weightData, lossData) {
var canvas = document.getElementById('weightChart');
var ctx = canvas.getContext('2d');
// Reset canvas size for high DPI
var dpr = window.devicePixelRatio || 1;
var rect = canvas.getBoundingClientRect();
canvas.width = rect.width * dpr;
canvas.height = rect.height * dpr;
ctx.scale(dpr, dpr);
var width = rect.width;
var height = rect.height;
var padding = 40;
var graphWidth = width – (padding * 2);
var graphHeight = height – (padding * 2);
// Clear canvas
ctx.clearRect(0, 0, width, height);
// Helper to map values
var maxWeight = Math.max.apply(null, weightData) * 1.05;
var minWeight = Math.min.apply(null, weightData) * 0.9;
var range = maxWeight – minWeight;
function getX(index) {
return padding + (index * (graphWidth / (labels.length – 1)));
}
function getY(val) {
return height – padding – ((val – minWeight) / range * graphHeight);
}
// Draw Grid & Labels
ctx.beginPath();
ctx.strokeStyle = '#eee';
ctx.lineWidth = 1;
ctx.font = '12px Arial';
ctx.fillStyle = '#666';
ctx.textAlign = 'center';
// X Axis
for(var i=0; i<labels.length; i++) {
var x = getX(i);
ctx.fillText(labels[i], x, height – 10);
ctx.moveTo(x, padding);
ctx.lineTo(x, height – padding);
}
ctx.stroke();
// Y Axis Labels (Approx 5 steps)
ctx.textAlign = 'right';
for(var j=0; j<=5; j++) {
var val = minWeight + (range * (j/5));
var y = getY(val);
ctx.fillText(Math.round(val), padding – 10, y + 4);
}
// Draw Weight Line (Primary)
ctx.beginPath();
ctx.strokeStyle = '#004a99';
ctx.lineWidth = 3;
ctx.moveTo(getX(0), getY(weightData[0]));
for(var k=1; k<weightData.length; k++) {
ctx.lineTo(getX(k), getY(weightData[k]));
}
ctx.stroke();
// Draw Points
for(var m=0; m<weightData.length; m++) {
var px = getX(m);
var py = getY(weightData[m]);
ctx.beginPath();
ctx.arc(px, py, 5, 0, 2 * Math.PI);
ctx.fillStyle = '#fff';
ctx.fill();
ctx.lineWidth = 2;
ctx.stroke();
}
// Legend
ctx.fillStyle = '#004a99';
ctx.font = 'bold 12px Arial';
ctx.textAlign = 'left';
ctx.fillText("Predicted Weight Trend", padding, 20);
}
function resetCalculator() {
document.getElementById('gender').value = 'female';
document.getElementById('heightFt').value = '5';
document.getElementById('heightIn').value = '4';
document.getElementById('currentWeight').value = '280';
document.getElementById('surgeryType').value = 'bypass';
calculateResults();
}
function copyResults() {
var weight12 = document.getElementById('result12Month').innerText;
var totalLoss = document.getElementById('totalLossResult').innerText;
var surgery = document.getElementById('surgeryType').options[document.getElementById('surgeryType').selectedIndex].text;
var text = "Bariatric Weight Loss Projection:\n" +
"Surgery: " + surgery + "\n" +
"Predicted Weight at 12 Months: " + weight12 + "\n" +
"Total Expected Loss (18 mo): " + totalLoss + "\n\n" +
"Generated by Bariatric Weight Loss Calculator";
// Create temporary textarea to copy
var tempInput = document.createElement("textarea");
tempInput.value = text;
document.body.appendChild(tempInput);
tempInput.select();
document.execCommand("copy");
document.body.removeChild(tempInput);
var btn = document.querySelector('.btn-copy');
var originalText = btn.innerText;
btn.innerText = "Copied!";
setTimeout(function() {
btn.innerText = originalText;
}, 2000);
}
// Handle Resize
window.addEventListener('resize', function() {
calculateResults();
});