Calculate your current pregnancy progress and estimated due date based on your last menstrual period (LMP).
Gestational Age:
Estimated Due Date (EDD):
Current Trimester:
Days Remaining:
Understanding Estimated Gestational Age (EGA)
Gestational age is the common term used during pregnancy to describe how far along the pregnancy is. It is measured in weeks, from the first day of the woman's last menstrual cycle to the current date. A normal pregnancy can range from 38 to 42 weeks.
How the Calculation Works
The most standard method for calculating EGA is based on the Last Menstrual Period (LMP). This method assumes that conception occurred on day 14 of the cycle. While many women do not conceive exactly on day 14, this 40-week model provides a standardized timeline for prenatal care.
Naegele's Rule: A standard way of calculating the due date. It involves adding one year, subtracting three months, and adding seven days to the first day of a woman's last menstrual period.
Cycle Adjustment: If your average cycle is longer or shorter than the standard 28 days, the calculation should be adjusted to reflect when ovulation likely occurred.
Pregnancy Milestones by Trimester
Pregnancy is traditionally divided into three trimesters:
First Trimester (0 – 13 weeks): This is the period of rapid development where the basic structures of the body and organs are formed.
Second Trimester (14 – 26 weeks): Often called the "golden period," many of the early pregnancy symptoms like morning sickness fade away.
Third Trimester (27 – 40+ weeks): The final stretch where the baby grows significantly in size and weight, preparing for life outside the womb.
Why EGA Matters
Knowing the exact gestational age is crucial for several medical reasons:
Prenatal Screening: Many tests, such as the quad screen or anatomy ultrasound, must be performed at very specific gestational windows.
Growth Tracking: Doctors use EGA to ensure the fetus is hitting growth milestones appropriately.
Management of Complications: If complications arise, the gestational age determines the viability of the fetus and the course of medical intervention.
Note: This calculator is for educational purposes only. Please consult with a healthcare professional for an official clinical dating of your pregnancy, which may include an ultrasound for higher accuracy.
function calculateEGA() {
var lmpInput = document.getElementById('lmpDate').value;
var cycleLength = parseInt(document.getElementById('cycleLength').value);
var errorDiv = document.getElementById('egaError');
var resultsDiv = document.getElementById('egaResults');
// Reset display
errorDiv.style.display = 'none';
resultsDiv.style.display = 'none';
if (!lmpInput) {
errorDiv.innerHTML = "Please select a valid Last Menstrual Period date.";
errorDiv.style.display = 'block';
return;
}
var lmpDate = new Date(lmpInput);
var today = new Date();
// Ensure time is set to midnight for accurate day calculation
today.setHours(0, 0, 0, 0);
lmpDate.setHours(0, 0, 0, 0);
if (lmpDate > today) {
errorDiv.innerHTML = "LMP date cannot be in the future.";
errorDiv.style.display = 'block';
return;
}
// Standard pregnancy is 280 days from LMP based on 28-day cycle
// Adjust for cycle length: add (cycleLength – 28)
var cycleAdjustment = cycleLength – 28;
// Calculate Total Days passed
var diffTime = Math.abs(today – lmpDate);
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
// Apply cycle adjustment to the relative age
// (If cycle is 30 days, ovulation was 2 days later, so baby is 2 days "younger")
var adjustedDaysPassed = diffDays – cycleAdjustment;
if (adjustedDaysPassed 300) {
errorDiv.innerHTML = "The date entered exceeds a standard 42-week pregnancy range. Please check the date.";
errorDiv.style.display = 'block';
return;
}
var weeks = Math.floor(adjustedDaysPassed / 7);
var days = adjustedDaysPassed % 7;
// Calculate Due Date (280 days + cycle adjustment)
var eddDate = new Date(lmpDate);
eddDate.setDate(eddDate.getDate() + 280 + cycleAdjustment);
// Days remaining
var remainingTime = eddDate – today;
var remainingDays = Math.ceil(remainingTime / (1000 * 60 * 60 * 24));
if (remainingDays < 0) remainingDays = 0;
// Determine Trimester
var trimester = "";
if (weeks < 14) {
trimester = "First Trimester";
} else if (weeks < 27) {
trimester = "Second Trimester";
} else {
trimester = "Third Trimester";
}
// Formatting Due Date
var options = { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' };
var formattedDue = eddDate.toLocaleDateString(undefined, options);
// Display Results
document.getElementById('resAge').innerHTML = weeks + " Weeks, " + days + " Days";
document.getElementById('resDue').innerHTML = formattedDue;
document.getElementById('resTrimester').innerHTML = trimester;
document.getElementById('resRemaining').innerHTML = remainingDays + " Days";
resultsDiv.style.display = 'block';
}