Estimate your baby's arrival date using your Last Menstrual Period, Conception Date, or IVF Transfer Date.
Choose Your Calculation Method:
This is the most common method. Enter the first day of your last period.
Default is 28 days. Adjust if your cycle is typically shorter or longer.
Only use this if you know the exact date of conception (e.g., from ovulation tracking).
Select Age
3-Day Embryo (Cleavage Stage)
5-Day Embryo (Blastocyst Stage)
Specify if the embryo was 3 or 5 days old when transferred.
Your Estimated Due Date:
Trimester Breakdown:
function toggleInputs() {
var methodLMP = document.getElementById("methodLMP").checked;
var methodConception = document.getElementById("methodConception").checked;
var methodIVF = document.getElementById("methodIVF").checked;
document.getElementById("lmpInputs").style.display = methodLMP ? "block" : "none";
document.getElementById("conceptionInputs").style.display = methodConception ? "block" : "none";
document.getElementById("ivfInputs").style.display = methodIVF ? "block" : "none";
// Clear inputs when switching methods to prevent accidental use of old data
if (!methodLMP) {
document.getElementById("lmpDate").value = "";
document.getElementById("cycleLength").value = "28";
}
if (!methodConception) {
document.getElementById("conceptionDate").value = "";
}
if (!methodIVF) {
document.getElementById("ivfTransferDate").value = "";
document.getElementById("embryoAge").value = "";
}
document.getElementById("result").style.display = "none"; // Hide results when method changes
}
function calculateDueDate() {
var dueDate = null;
var startDateForWeeks = null; // This will be the effective start of pregnancy (LMP equivalent)
var methodLMP = document.getElementById("methodLMP").checked;
var methodConception = document.getElementById("methodConception").checked;
var methodIVF = document.getElementById("methodIVF").checked;
var today = new Date();
today.setHours(0, 0, 0, 0); // Normalize today's date
if (methodLMP) {
var lmpDateStr = document.getElementById("lmpDate").value;
var cycleLengthStr = document.getElementById("cycleLength").value;
if (!lmpDateStr) {
alert("Please enter the First Day of your Last Menstrual Period.");
return;
}
var lmpDate = new Date(lmpDateStr + 'T00:00:00'); // Ensure UTC interpretation for consistency
if (isNaN(lmpDate.getTime())) {
alert("Invalid LMP Date. Please use a valid date format.");
return;
}
var cycleLength = parseInt(cycleLengthStr);
if (isNaN(cycleLength) || cycleLength 45) {
alert("Please enter a valid average cycle length (20-45 days).");
return;
}
// Naegele's Rule: LMP + 280 days. Adjust for cycle length: + (cycleLength – 28) days
dueDate = new Date(lmpDate.getTime());
dueDate.setDate(dueDate.getDate() + 280 + (cycleLength – 28));
startDateForWeeks = new Date(lmpDate.getTime()); // LMP is week 1 day 0
} else if (methodConception) {
var conceptionDateStr = document.getElementById("conceptionDate").value;
if (!conceptionDateStr) {
alert("Please enter the Conception Date.");
return;
}
var conceptionDate = new Date(conceptionDateStr + 'T00:00:00');
if (isNaN(conceptionDate.getTime())) {
alert("Invalid Conception Date. Please use a valid date format.");
return;
}
// Conception Date + 266 days (38 weeks)
dueDate = new Date(conceptionDate.getTime());
dueDate.setDate(dueDate.getDate() + 266);
// LMP equivalent for conception date is 14 days before conception
startDateForWeeks = new Date(conceptionDate.getTime());
startDateForWeeks.setDate(startDateForWeeks.getDate() – 14);
} else if (methodIVF) {
var ivfTransferDateStr = document.getElementById("ivfTransferDate").value;
var embryoAgeStr = document.getElementById("embryoAge").value;
if (!ivfTransferDateStr) {
alert("Please enter the IVF Transfer Date.");
return;
}
var ivfTransferDate = new Date(ivfTransferDateStr + 'T00:00:00');
if (isNaN(ivfTransferDate.getTime())) {
alert("Invalid IVF Transfer Date. Please use a valid date format.");
return;
}
if (!embryoAgeStr) {
alert("Please select the Embryo Age at Transfer.");
return;
}
var embryoAge = parseInt(embryoAgeStr);
// IVF Calculation:
// 3-day embryo: Transfer Date + 263 days (38 weeks – 3 days)
// 5-day embryo: Transfer Date + 261 days (38 weeks – 5 days)
dueDate = new Date(ivfTransferDate.getTime());
if (embryoAge === 3) {
dueDate.setDate(dueDate.getDate() + 263);
// LMP equivalent for 3-day embryo transfer is 17 days before transfer
startDateForWeeks = new Date(ivfTransferDate.getTime());
startDateForWeeks.setDate(startDateForWeeks.getDate() – 17);
} else if (embryoAge === 5) {
dueDate.setDate(dueDate.getDate() + 261);
// LMP equivalent for 5-day embryo transfer is 19 days before transfer
startDateForWeeks = new Date(ivfTransferDate.getTime());
startDateForWeeks.setDate(startDateForWeeks.getDate() – 19);
} else {
alert("Invalid embryo age selected.");
return;
}
} else {
alert("Please select a calculation method.");
return;
}
if (!dueDate || isNaN(dueDate.getTime())) {
alert("Could not calculate due date. Please check your inputs.");
return;
}
// Format due date for display
var options = { year: 'numeric', month: 'long', day: 'numeric' };
document.getElementById("dueDateOutput").innerHTML = dueDate.toLocaleDateString('en-US', options);
// Calculate current week of pregnancy
if (startDateForWeeks && startDateForWeeks today) {
document.getElementById("pregnancyWeekOutput").innerHTML = "Pregnancy has not yet started based on your input date.";
} else {
document.getElementById("pregnancyWeekOutput").innerHTML = "Cannot determine current week without a valid start date.";
}
// Calculate days remaining
var daysRemaining = Math.ceil((dueDate.getTime() – today.getTime()) / (1000 * 60 * 60 * 24));
if (daysRemaining < 0) {
document.getElementById("daysRemainingOutput").innerHTML = "Your baby was due " + Math.abs(daysRemaining) + " days ago!";
} else {
document.getElementById("daysRemainingOutput").innerHTML = daysRemaining + " days remaining until your due date.";
}
// Calculate trimesters
if (startDateForWeeks) {
var trimester1End = new Date(startDateForWeeks.getTime());
trimester1End.setDate(trimester1End.getDate() + (13 * 7) -1); // End of week 13
var trimester2End = new Date(startDateForWeeks.getTime());
trimester2End.setDate(trimester2End.getDate() + (27 * 7) -1); // End of week 27
document.getElementById("trimester1Output").innerHTML = "First Trimester: " + startDateForWeeks.toLocaleDateString('en-US', options) + " – " + trimester1End.toLocaleDateString('en-US', options);
document.getElementById("trimester2Output").innerHTML = "Second Trimester: " + new Date(trimester1End.getTime() + (1000 * 60 * 60 * 24)).toLocaleDateString('en-US', options) + " – " + trimester2End.toLocaleDateString('en-US', options);
document.getElementById("trimester3Output").innerHTML = "Third Trimester: " + new Date(trimester2End.getTime() + (1000 * 60 * 60 * 24)).toLocaleDateString('en-US', options) + " – " + dueDate.toLocaleDateString('en-US', options);
} else {
document.getElementById("trimester1Output").innerHTML = "Trimester dates cannot be calculated without a valid start date.";
document.getElementById("trimester2Output").innerHTML = "";
document.getElementById("trimester3Output").innerHTML = "";
}
document.getElementById("result").style.display = "block";
}
// Initialize inputs on page load
window.onload = function() {
toggleInputs();
// Set default LMP date to a realistic past date for example
var defaultLMP = new Date();
defaultLMP.setDate(defaultLMP.getDate() – (10 * 7)); // 10 weeks ago
document.getElementById("lmpDate").valueAsDate = defaultLMP;
};
Understanding Your Pregnancy Due Date
A pregnancy due date calculator is a tool used to estimate when your baby is likely to be born. While it provides a target date, it's important to remember that only about 4% of babies are born exactly on their due date. Most babies arrive between 37 and 42 weeks of gestation.
How is the Due Date Calculated?
There are several common methods to estimate a due date, and this calculator offers the most widely used options:
1. Last Menstrual Period (LMP) – Naegele's Rule
This is the most common method. It assumes a 28-day menstrual cycle with ovulation occurring on day 14. The calculation involves adding 280 days (40 weeks) to the first day of your last menstrual period. If your cycle is longer or shorter than 28 days, the calculator adjusts this by adding or subtracting the difference from 28 days to the 280-day total.
Example: If your LMP was January 1, 2024, and you have a 28-day cycle, your due date would be around October 8, 2024 (January 1 + 280 days).
Example with Adjusted Cycle: If your LMP was January 1, 2024, and you have a 30-day cycle, the calculation adds an extra 2 days (30-28) to the 280 days, making your due date around October 10, 2024.
2. Conception Date
If you know the exact date you conceived (e.g., through ovulation tracking or IVF), this method can be more precise. The due date is calculated by adding 266 days (38 weeks) to your conception date. This is because pregnancy is typically 40 weeks from LMP, but conception usually occurs around 2 weeks after LMP.
Example: If you conceived on January 15, 2024, your due date would be around October 8, 2024 (January 15 + 266 days).
3. IVF Transfer Date
For pregnancies conceived via In Vitro Fertilization (IVF), the transfer date and the age of the embryo are used. This method is often considered very accurate because the exact date of conception (or fertilization) is known.
For a 3-day embryo transfer: Add 263 days to the transfer date. (38 weeks – 3 days)
For a 5-day embryo transfer (blastocyst): Add 261 days to the transfer date. (38 weeks – 5 days)
Example (3-day embryo): If your 3-day embryo was transferred on January 20, 2024, your due date would be around October 10, 2024 (January 20 + 263 days).
Example (5-day embryo): If your 5-day embryo was transferred on January 20, 2024, your due date would be around October 8, 2024 (January 20 + 261 days).
What are Trimesters?
Pregnancy is divided into three trimesters, each marked by specific developmental milestones for the baby and changes for the mother. While the exact week ranges can vary slightly, they are generally:
First Trimester: Week 1 to Week 13
Second Trimester: Week 14 to Week 27
Third Trimester: Week 28 to Week 40 (or delivery)
Knowing which trimester you are in helps you understand what to expect in terms of symptoms, prenatal care, and baby development.
Important Considerations
Estimates, Not Guarantees: Your due date is an estimate. Your baby will arrive when they are ready!
Ultrasound Confirmation: Early ultrasounds (especially in the first trimester) can provide a more accurate due date, as they measure the baby's size to estimate gestational age. Your healthcare provider may adjust your due date based on these scans.
Irregular Periods: If you have very irregular periods, the LMP method may not be accurate. In such cases, an early ultrasound or conception date (if known) will be more reliable.
Always consult with your healthcare provider for personalized advice and the most accurate information regarding your pregnancy.