This calculator helps you estimate your baby's due date and conception date based on either your last menstrual period (LMP) or a known conception date. Please note that these dates are estimates, and your baby may arrive earlier or later than predicted.
Calculate from Last Menstrual Period (LMP)
Calculate from Known Conception Date
function formatDate(date) {
var options = { year: 'numeric', month: 'long', day: 'numeric' };
return date.toLocaleDateString('en-US', options);
}
function calculateFromLMP() {
var lmpDateInput = document.getElementById("lmpDate").value;
var lmpResultDiv = document.getElementById("lmpResult");
lmpResultDiv.style.display = "none";
lmpResultDiv.innerHTML = "";
if (!lmpDateInput) {
lmpResultDiv.innerHTML = "Please enter your Last Menstrual Period (LMP) start date.";
lmpResultDiv.style.display = "block";
return;
}
var lmp = new Date(lmpDateInput);
if (isNaN(lmp.getTime())) {
lmpResultDiv.innerHTML = "Invalid LMP date entered. Please use a valid date format.";
lmpResultDiv.style.display = "block";
return;
}
// Calculate Estimated Due Date (EDD) using Naegele's Rule: LMP + 280 days (40 weeks)
var edd = new Date(lmp.getTime());
edd.setDate(edd.getDate() + 280);
// Calculate Estimated Conception Date: LMP + 14 days (assuming ovulation on day 14)
var conceptionDate = new Date(lmp.getTime());
conceptionDate.setDate(conceptionDate.getDate() + 14);
lmpResultDiv.innerHTML =
"Estimated Due Date (EDD): " + formatDate(edd) + "" +
"Estimated Conception Date: " + formatDate(conceptionDate) + "" +
"(Based on a 28-day cycle with ovulation on day 14)";
lmpResultDiv.style.display = "block";
}
function calculateFromConception() {
var knownConceptionDateInput = document.getElementById("knownConceptionDate").value;
var conceptionResultDiv = document.getElementById("conceptionResult");
conceptionResultDiv.style.display = "none";
conceptionResultDiv.innerHTML = "";
if (!knownConceptionDateInput) {
conceptionResultDiv.innerHTML = "Please enter the known conception date.";
conceptionResultDiv.style.display = "block";
return;
}
var conception = new Date(knownConceptionDateInput);
if (isNaN(conception.getTime())) {
conceptionResultDiv.innerHTML = "Invalid conception date entered. Please use a valid date format.";
conceptionResultDiv.style.display = "block";
return;
}
// Calculate Estimated Due Date (EDD) from conception: Conception Date + 266 days (38 weeks)
var edd = new Date(conception.getTime());
edd.setDate(edd.getDate() + 266);
conceptionResultDiv.innerHTML =
"Estimated Due Date (EDD): " + formatDate(edd) + "" +
"(Based on 38 weeks from conception)";
conceptionResultDiv.style.display = "block";
}
Understanding Your Dates
When you're expecting, knowing your baby's due date and the approximate conception date can be incredibly exciting and helpful for planning. This calculator provides estimates based on common medical guidelines.
Estimated Due Date (EDD)
The Estimated Due Date (EDD), also known as the Estimated Date of Confinement (EDC), is the date your baby is expected to be born. It's typically calculated as 40 weeks (280 days) from the first day of your last menstrual period (LMP). This method is known as Naegele's Rule. However, only about 4% of babies are born exactly on their due date, with most arriving between 37 and 42 weeks of gestation.
Conception Date
The conception date is the actual date when fertilization occurred. If you know your LMP, the conception date is usually estimated to be about 14 days after the start of your LMP, assuming a typical 28-day menstrual cycle with ovulation occurring around day 14. If you know the exact date of conception (e.g., through IVF or precise tracking), your due date can be calculated as 266 days (38 weeks) from that date.
Why are these dates estimates?
Variations in Menstrual Cycles: Not all women have a perfect 28-day cycle, and ovulation can vary.
Individual Differences: Every pregnancy is unique, and babies develop at slightly different rates.
External Factors: Factors like stress, diet, and health can influence ovulation and implantation.
While these calculations provide a good starting point, your healthcare provider will use additional information, such as early ultrasound scans, to confirm and refine your due date. Ultrasounds are often considered the most accurate method for dating a pregnancy, especially if performed in the first trimester.