Calculate your current week of pregnancy and estimated due date based on your last period or conception date.
Last Menstrual Period (LMP)
Date of Conception
Known Due Date
Estimated Due Date:
Current Trimester:
Progress:
Days Remaining:
How Your Pregnancy Weeks Are Calculated
Medical professionals usually calculate pregnancy based on the first day of your Last Menstrual Period (LMP). This is because most women don't know the exact date of conception, but they do remember when their last period started. Under this system, you are actually considered "pregnant" about two weeks before the baby is even conceived!
Understanding the Three Trimesters
A typical pregnancy lasts about 40 weeks (280 days) from the LMP. These are divided into three stages:
Trimester
Time Period
Key Development
First Trimester
0 to 13 Weeks
Organ formation and rapid cell division.
Second Trimester
14 to 26 Weeks
The "Golden Period" where the baby grows and begins moving.
Third Trimester
27 to 40 Weeks
Final growth, lung development, and preparation for birth.
Example Calculation
If your last period started on January 1st and you have a 28-day cycle:
Due Date: October 8th (Approximately 280 days later).
Conception: Occurred around January 15th.
Week 12: You would reach this milestone around March 26th.
Frequently Asked Questions
Is the due date guaranteed?
No. Only about 4% of babies are born on their exact due date. Most are born between 37 and 42 weeks.
What if my cycle is longer than 28 days?
If your cycle is 35 days, you likely ovulated a week later than average. Our calculator adjusts the due date by adding those extra days to the standard 280-day count.
function toggleCycleInput() {
var method = document.getElementById("calcMethod").value;
var label = document.getElementById("dateLabel");
var cycleGroup = document.getElementById("cycleGroup");
if (method === "lmp") {
label.innerText = "First Day of Last Period";
cycleGroup.style.display = "block";
} else if (method === "conception") {
label.innerText = "Date of Conception";
cycleGroup.style.display = "none";
} else {
label.innerText = "Confirmed Due Date";
cycleGroup.style.display = "none";
}
}
function calculatePregnancy() {
var method = document.getElementById("calcMethod").value;
var inputDateValue = document.getElementById("dateInput").value;
var cycleLength = parseInt(document.getElementById("cycleLength").value) || 28;
if (!inputDateValue) {
alert("Please select a date.");
return;
}
var inputDate = new Date(inputDateValue);
var today = new Date();
var edd;
var startDate;
if (method === "lmp") {
// Standard Naegele's Rule adjustment for cycle length
// Standard is 280 days from LMP for a 28 day cycle
var adjustment = cycleLength – 28;
edd = new Date(inputDate);
edd.setDate(edd.getDate() + 280 + adjustment);
startDate = new Date(inputDate);
} else if (method === "conception") {
// Conception is typically 266 days before birth
edd = new Date(inputDate);
edd.setDate(edd.getDate() + 266);
startDate = new Date(inputDate);
startDate.setDate(startDate.getDate() – 14); // Adjust to LMP-equivalent
} else {
// Based on due date
edd = new Date(inputDate);
startDate = new Date(edd);
startDate.setDate(startDate.getDate() – 280);
}
// Calculate difference in milliseconds
var diffTime = today.getTime() – startDate.getTime();
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
var weeks = Math.floor(diffDays / 7);
var days = diffDays % 7;
// Safety check for future dates or extreme past
if (diffDays = 42) {
document.getElementById("currentStageText").innerText = "Post-term (42+ Weeks)";
} else {
document.getElementById("currentStageText").innerText = "You are " + weeks + " weeks and " + days + " days pregnant";
}
document.getElementById("eddResult").innerText = edd.toLocaleDateString('en-US', { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' });
var trimester = "";
if (weeks < 14) trimester = "First Trimester";
else if (weeks 0 ? daysLeft : 0) + " Days";
// Scroll to results
document.getElementById("results").scrollIntoView({ behavior: 'smooth', block: 'nearest' });
}