Choose your preferred method to estimate your baby's due date:
— Select a method —
Last Menstrual Period (LMP)
Conception Date
IVF Transfer Date
3-Day Embryo
5-Day Embryo (Blastocyst)
function showHideInputs() {
var method = document.getElementById("calculationMethod").value;
document.getElementById("lmpInputs").style.display = "none";
document.getElementById("conceptionInputs").style.display = "none";
document.getElementById("ivfInputs").style.display = "none";
if (method === "lmp") {
document.getElementById("lmpInputs").style.display = "block";
} else if (method === "conception") {
document.getElementById("conceptionInputs").style.display = "block";
} else if (method === "ivf") {
document.getElementById("ivfInputs").style.display = "block";
}
document.getElementById("result").innerHTML = ""; // Clear previous results
}
function calculateDueDate() {
var method = document.getElementById("calculationMethod").value;
var dueDate = null;
var calculationBasis = "";
var today = new Date();
today.setHours(0, 0, 0, 0); // Normalize today's date to midnight for consistent day calculations
var gestationalAgeHtml = "";
if (method === "lmp") {
var lmpDateStr = document.getElementById("lmpDate").value;
if (!lmpDateStr) {
document.getElementById("result").innerHTML = "Please enter your Last Menstrual Period (LMP) date.";
return;
}
var lmp = new Date(lmpDateStr + "T00:00:00"); // Use T00:00:00 to ensure UTC interpretation
if (isNaN(lmp.getTime())) {
document.getElementById("result").innerHTML = "Invalid LMP date. Please use a valid date format.";
return;
}
dueDate = new Date(lmp.getTime());
dueDate.setDate(dueDate.getDate() + 280); // 40 weeks (280 days) from LMP
calculationBasis = "Based on your Last Menstrual Period (LMP)";
// Calculate current gestational age
var timeDiff = today.getTime() – lmp.getTime();
var daysPregnant = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
if (daysPregnant >= 0) { // Only show if LMP is not in the future
var weeksPregnant = Math.floor(daysPregnant / 7);
var remainingDays = daysPregnant % 7;
gestationalAgeHtml = "You are approximately " + weeksPregnant + " weeks and " + remainingDays + " days pregnant.";
}
} else if (method === "conception") {
var conceptionDateStr = document.getElementById("conceptionDate").value;
if (!conceptionDateStr) {
document.getElementById("result").innerHTML = "Please enter your Conception Date.";
return;
}
var conception = new Date(conceptionDateStr + "T00:00:00");
if (isNaN(conception.getTime())) {
document.getElementById("result").innerHTML = "Invalid Conception Date. Please use a valid date format.";
return;
}
dueDate = new Date(conception.getTime());
dueDate.setDate(dueDate.getDate() + 266); // 38 weeks (266 days) from conception
calculationBasis = "Based on your estimated Conception Date";
// Calculate current gestational age
var timeDiff = today.getTime() – conception.getTime();
var daysPregnant = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
if (daysPregnant >= 0) {
var weeksPregnant = Math.floor(daysPregnant / 7);
var remainingDays = daysPregnant % 7;
gestationalAgeHtml = "You are approximately " + weeksPregnant + " weeks and " + remainingDays + " days pregnant (from conception).";
}
} else if (method === "ivf") {
var transferDateStr = document.getElementById("ivfTransferDate").value;
var embryoAge = parseInt(document.getElementById("embryoAge").value);
if (!transferDateStr) {
document.getElementById("result").innerHTML = "Please enter your IVF Transfer Date.";
return;
}
var transfer = new Date(transferDateStr + "T00:00:00");
if (isNaN(transfer.getTime())) {
document.getElementById("result").innerHTML = "Invalid IVF Transfer Date. Please use a valid date format.";
return;
}
dueDate = new Date(transfer.getTime());
dueDate.setDate(dueDate.getDate() + (266 – embryoAge)); // 38 weeks (266 days) from conception, adjusted for embryo age
calculationBasis = "Based on your IVF Transfer Date and " + embryoAge + "-day embryo";
// Calculate current gestational age
var timeDiff = today.getTime() – transfer.getTime();
var daysSinceTransfer = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
var daysPregnant = daysSinceTransfer + embryoAge; // Add embryo age to days since transfer
if (daysPregnant >= 0) {
var weeksPregnant = Math.floor(daysPregnant / 7);
var remainingDays = daysPregnant % 7;
gestationalAgeHtml = "You are approximately " + weeksPregnant + " weeks and " + remainingDays + " days pregnant (from transfer date adjusted for embryo age).";
}
} else {
document.getElementById("result").innerHTML = "Please select a calculation method.";
return;
}
if (dueDate) {
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedDueDate = dueDate.toLocaleDateString('en-US', options);
var resultHtml = "Your estimated due date is: " + formattedDueDate + "";
resultHtml += "" + calculationBasis + ".";
if (gestationalAgeHtml) {
resultHtml += gestationalAgeHtml;
}
resultHtml += "Remember, this is an estimate. Only about 5% of babies are born on their exact due date.";
document.getElementById("result").innerHTML = resultHtml;
}
}
// Initialize display on page load
document.addEventListener('DOMContentLoaded', function() {
showHideInputs();
});
Understanding Your Due Date
An accurate due date is a crucial piece of information throughout your pregnancy journey. It helps healthcare providers monitor your baby's growth and development, schedule important tests, and plan for delivery. While no calculator can predict the exact day your baby will arrive, these tools provide a reliable estimate based on standard medical formulas.
How is the Due Date Calculated?
There are several methods used to estimate a due date, each with varying levels of accuracy depending on the information available:
1. Last Menstrual Period (LMP) – Naegele's Rule
This is the most common method. Pregnancy is typically considered to last 40 weeks (280 days) from the first day of your last menstrual period. Naegele's Rule involves adding 7 days to the first day of your LMP, then adding 9 months. Our calculator simplifies this by directly adding 280 days to your LMP date.
Example: If your LMP was January 1, 2024:
Add 7 days: January 8, 2024
Add 9 months: October 8, 2024
Using the 280-day method: January 1, 2024 + 280 days = October 8, 2024.
This method is most accurate for individuals with regular 28-day menstrual cycles.
2. Conception Date
If you know the exact date of conception (e.g., through ovulation tracking or timed intercourse), this method can be very precise. Pregnancy is considered 38 weeks (266 days) from conception. Our calculator adds 266 days to your specified conception date.
Example: If you conceived on January 15, 2024:
Add 266 days: January 15, 2024 + 266 days = October 8, 2024.
3. IVF Transfer Date
For pregnancies conceived through In Vitro Fertilization (IVF), the transfer date provides a very accurate starting point. The calculation adjusts based on the age of the embryo at the time of transfer:
For a 3-day embryo transfer: Add 263 days (266 – 3 days) to the transfer date.
For a 5-day embryo (blastocyst) transfer: Add 261 days (266 – 5 days) to the transfer date.
Example: If you had a 5-day embryo transferred on January 20, 2024:
Add 261 days: January 20, 2024 + 261 days = October 8, 2024.
4. Ultrasound Scan
While not a method our calculator can perform, early ultrasound scans (especially between 8 and 13 weeks) are often considered the most accurate way to determine a due date. This is because fetal growth is very consistent in early pregnancy. Your healthcare provider will use measurements of the fetus to estimate gestational age and, subsequently, the due date.
Why is it an "Estimate"?
It's important to remember that your due date is an estimate, not a deadline. Only about 5% of babies are born on their exact due date. Most babies arrive between 37 and 42 weeks of gestation. Factors like individual variations in cycle length, ovulation timing, and fetal growth can influence the actual birth date.
Always discuss your due date with your healthcare provider, as they will use all available information, including clinical assessments and ultrasound findings, to provide the most accurate estimate for your pregnancy.