Last Menstrual Period (LMP)
Estimated Due Date
Conception Date
0 Weeks, 0 Days
First Trimester
How to Calculate How Many Weeks Pregnant You Are
Understanding your gestational age is one of the first steps in your pregnancy journey. Most healthcare providers measure pregnancy starting from the first day of your last menstrual period (LMP). Even though you aren't technically pregnant for the first two weeks of this cycle, this standard method provides a consistent baseline for tracking fetal development.
Example Calculation:
If your Last Menstrual Period (LMP) started on January 1st and today is February 12th:
– Total days elapsed: 42 days
– Calculation: 42 / 7 = 6 weeks
– Result: You are 6 weeks and 0 days pregnant.
The Three Trimesters of Pregnancy
A typical pregnancy lasts approximately 40 weeks and is divided into three distinct stages:
First Trimester (Weeks 1-13): This is a period of rapid cellular division and organ formation. Many women experience morning sickness and fatigue during this phase.
Second Trimester (Weeks 14-27): Often called the "honeymoon phase," many symptoms subside, and you will likely start feeling the baby move (quickening).
Third Trimester (Weeks 28-40+): The final stretch where the baby gains weight rapidly and prepares for birth.
Common Calculation Methods
While the LMP method is the most common, there are other ways to determine how far along you are:
Conception Date: If you know the exact date of conception (often used in IVF or tracked ovulation), you add 2 weeks (14 days) to that date to get your gestational age.
Ultrasound Dating: In the first trimester, a crown-rump length (CRL) measurement via ultrasound is the most accurate way to determine the age of the fetus.
Due Date (EDD): If you already have an assigned due date from your doctor, you can work backward. A full-term pregnancy is considered 280 days from the LMP.
Why Knowing Your Exact Week Matters
Tracking your weeks is crucial for scheduling prenatal screenings, such as the Nuchal Translucency scan or the anatomy scan. It also helps you understand which developmental milestones your baby is reaching, from the first heartbeat to the development of fingernails and lung maturity.
function updateLabel() {
var method = document.getElementById('calcMethod').value;
var label = document.getElementById('dateLabel');
if (method === 'LMP') {
label.innerText = 'First Day of Last Period';
} else if (method === 'EDD') {
label.innerText = 'Your Estimated Due Date';
} else {
label.innerText = 'Date of Conception';
}
}
function calculatePregnancy() {
var dateVal = document.getElementById('inputDate').value;
if (!dateVal) {
alert('Please select a date.');
return;
}
var method = document.getElementById('calcMethod').value;
var selectedDate = new Date(dateVal);
var today = new Date();
today.setHours(0, 0, 0, 0);
var totalDays = 0;
var eddDate = new Date();
if (method === 'LMP') {
var diffTime = today – selectedDate;
totalDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
eddDate = new Date(selectedDate.getTime() + (280 * 24 * 60 * 60 * 1000));
} else if (method === 'EDD') {
var diffTime = selectedDate – today;
var daysRemaining = Math.floor(diffTime / (1000 * 60 * 60 * 24));
totalDays = 280 – daysRemaining;
eddDate = selectedDate;
} else if (method === 'CONC') {
var diffTime = today – selectedDate;
totalDays = Math.floor(diffTime / (1000 * 60 * 60 * 24)) + 14;
eddDate = new Date(selectedDate.getTime() + (266 * 24 * 60 * 60 * 1000));
}
if (totalDays 300) {
alert('The date entered indicates a pregnancy longer than 43 weeks. Please check your dates.');
return;
}
var weeks = Math.floor(totalDays / 7);
var days = totalDays % 7;
// Trimester Logic
var trimester = "";
if (weeks < 14) {
trimester = "First Trimester";
} else if (weeks 100) progressPercent = 100;
// Display Results
document.getElementById('preg-result-area').style.display = 'block';
document.getElementById('resultWeeks').innerText = weeks + " Weeks, " + days + " Days";
document.getElementById('trimesterTag').innerText = trimester;
document.getElementById('progressBar').style.width = progressPercent + "%";
document.getElementById('resultEDD').innerText = "Estimated Due Date: " + eddDate.toDateString();
var daysToDue = Math.floor((eddDate – today) / (1000 * 60 * 60 * 24));
if (daysToDue > 0) {
document.getElementById('resultDaysToGo').innerText = daysToDue + " days to go!";
} else {
document.getElementById('resultDaysToGo').innerText = "You have reached your due date!";
}
}