.fet-calc-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 20px auto;
padding: 30px;
border: 1px solid #e1e8ed;
border-radius: 12px;
background-color: #ffffff;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
color: #333;
}
.fet-calc-header {
text-align: center;
margin-bottom: 30px;
}
.fet-calc-header h2 {
color: #2c3e50;
margin-bottom: 10px;
}
.fet-calc-form {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
margin-bottom: 25px;
}
.fet-input-group {
display: flex;
flex-direction: column;
}
.fet-input-group label {
font-weight: 600;
margin-bottom: 8px;
font-size: 14px;
color: #555;
}
.fet-input-group input, .fet-input-group select {
padding: 12px;
border: 1px solid #ccd6dd;
border-radius: 6px;
font-size: 16px;
}
.fet-calc-btn {
grid-column: span 2;
background-color: #ff6b6b;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 6px;
cursor: pointer;
transition: background-color 0.2s;
}
.fet-calc-btn:hover {
background-color: #ee5253;
}
.fet-result-box {
margin-top: 30px;
padding: 20px;
background-color: #f8f9fa;
border-radius: 8px;
border-left: 5px solid #ff6b6b;
display: none;
}
.fet-result-box h3 {
margin-top: 0;
color: #2c3e50;
}
.fet-result-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 15px;
margin-top: 15px;
}
.fet-result-item {
background: white;
padding: 10px;
border-radius: 4px;
box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}
.fet-result-label {
font-size: 12px;
color: #777;
display: block;
}
.fet-result-value {
font-size: 18px;
font-weight: bold;
color: #ff6b6b;
}
.fet-article {
margin-top: 40px;
line-height: 1.6;
color: #444;
}
.fet-article h3 {
color: #2c3e50;
border-bottom: 2px solid #f1f1f1;
padding-bottom: 10px;
}
@media (max-width: 600px) {
.fet-calc-form, .fet-result-grid {
grid-template-columns: 1fr;
}
.fet-calc-btn {
grid-column: span 1;
}
}
Your Estimated Timeline
Estimated Due Date
–
Current Progress
–
Equivalent LMP Date
–
End of 1st Trimester
–
How a FET Due Date is Calculated
Unlike a natural conception where the due date is calculated based on the first day of your last menstrual period (LMP), a Frozen Embryo Transfer (FET) provides a more precise starting point. Because the exact timing of the embryo development and the transfer is known, the "guesswork" of ovulation is removed.
To calculate the due date for an IVF pregnancy using a frozen embryo, we use the following formula:
- Day 3 FET: Transfer Date + 266 days – 3 days
- Day 5 FET: Transfer Date + 266 days – 5 days
- Day 6 FET: Transfer Date + 266 days – 6 days
Understanding the IVF Timeline
In a standard 40-week pregnancy, "conception" is technically considered to occur at the end of week 2. In IVF, the embryo age (Day 3 or Day 5) represents how many days post-fertilization the embryo was when it was frozen. Therefore, a Day 5 blastocyst transfer happens exactly at "3 weeks and 5 days" of pregnancy on the day of transfer.
Example Calculation
If you have a Day 5 Blastocyst transferred on September 10th:
- We subtract 5 days from the transfer date to find the "conception" equivalent (September 5th).
- We subtract 14 more days to find the "IVF LMP" date (August 22nd).
- We add 40 weeks to that LMP date to arrive at the estimated due date of May 29th.
Is the FET Due Date Final?
While the FET date is highly accurate for calculating the biological age of the pregnancy, your OBGYN may adjust the date slightly based on early ultrasound measurements (crown-rump length). Most clinicians stick to the IVF-provided date as it is generally considered the "gold standard" for dating assisted reproductive pregnancies.
function calculateFETDueDate() {
var transferDateInput = document.getElementById('transferDate').value;
var embryoAge = parseInt(document.getElementById('embryoAge').value);
if (!transferDateInput) {
alert("Please select your transfer date.");
return;
}
var transferDate = new Date(transferDateInput);
// Formula: Due date is 266 days (38 weeks) from fertilization
// We adjust for the age of the embryo at transfer
var dueDate = new Date(transferDate);
var daysToAdd = 266 – embryoAge;
dueDate.setDate(transferDate.getDate() + daysToAdd);
// Calculate "Adjusted LMP" (14 days before fertilization)
var lmpDate = new Date(transferDate);
var lmpAdjustment = 14 + embryoAge;
lmpDate.setDate(transferDate.getDate() – lmpAdjustment);
// Calculate End of 1st Trimester (LMP + 13 weeks)
var trimesterDate = new Date(lmpDate);
trimesterDate.setDate(lmpDate.getDate() + 91);
// Calculate current progress
var today = new Date();
var diffTime = Math.abs(today – lmpDate);
var diffDays = Math.ceil(diffTime / (1000 * 60 * 60 * 24));
var weeks = Math.floor(diffDays / 7);
var days = diffDays % 7;
var progressStr = "";
if (today dueDate) {
progressStr = "Past due date";
} else {
progressStr = weeks + " weeks, " + days + " days";
}
// Formatting options
var options = { month: 'long', day: 'numeric', year: 'numeric' };
document.getElementById('resDueDate').innerText = dueDate.toLocaleDateString(undefined, options);
document.getElementById('resLMP').innerText = lmpDate.toLocaleDateString(undefined, options);
document.getElementById('resTrimester').innerText = trimesterDate.toLocaleDateString(undefined, options);
document.getElementById('resProgress').innerText = progressStr;
document.getElementById('fetResults').style.display = 'block';
}