Gestational age, also known as pregnancy dating, is the most common way to measure the duration of a pregnancy. It is calculated from the first day of the pregnant person's last menstrual period (LMP). A standard full-term pregnancy is considered to be 40 weeks (280 days) from the LMP.
This calculator uses the Estimated Due Date (EDD) and the current date to determine the current gestational age. The EDD is typically calculated by adding 40 weeks (280 days) to the first day of the last menstrual period. However, for the purpose of this calculator, we work backward from the EDD to find the current age.
How it Works:
Input 1: Estimated Due Date (EDD): This is the projected date of delivery. It's crucial for accurately calculating the remaining time and current stage of pregnancy.
Input 2: Today's Date: This is the date you want to know the gestational age for. It allows you to track progress throughout the pregnancy.
The Calculation Logic:
The calculator determines the number of days between the EDD and "Today's Date". This difference represents the time remaining until the due date. By subtracting this remaining time from the standard 40 weeks (280 days), we arrive at the current gestational age.
If "Today's Date" is after the EDD, the calculation will show how many days post-term the pregnancy is. The gestational age is calculated as:
Gestational Age (in days) = 280 - (Number of days from Today's Date to EDD)
The result is then typically presented in weeks and days.
Example Calculation:
Let's say your Estimated Due Date (EDD) is October 26, 2024 and Today's Date is July 18, 2024.
Number of days from July 18, 2024, to October 26, 2024:
Days remaining in July: 31 – 18 = 13 days
Days in August: 31 days
Days in September: 30 days
Days in October until EDD: 26 days
Total remaining days = 13 + 31 + 30 + 26 = 100 days
Gestational Age (in days) = 280 days (full term) – 100 days (remaining) = 180 days
Gestational Age (in weeks and days) = 180 days / 7 days/week = 25 weeks with a remainder of 5 days.
So, on July 18, 2024, the gestational age would be approximately 25 weeks and 5 days.
Why is Gestational Age Important?
Understanding gestational age is vital for:
Monitoring fetal development against standard milestones.
Scheduling prenatal appointments and tests.
Identifying potential risks associated with premature or post-term pregnancies.
Informing medical decisions regarding labor and delivery.
function calculateGestationalAge() {
var eddInput = document.getElementById("dueDate");
var todayInput = document.getElementById("currentDate");
var resultDiv = document.getElementById("calculationResult");
var edd = new Date(eddInput.value);
var today = new Date(todayInput.value);
// Check if dates are valid
if (isNaN(edd.getTime()) || isNaN(today.getTime())) {
resultDiv.innerHTML = "Please enter valid dates.";
return;
}
// Ensure today's date is not after the due date for calculation purpose initially
// We handle post-term separately if needed, but this calculation is for age *before* due date
if (today.getTime() > edd.getTime()) {
var timeDiff = today.getTime() – edd.getTime();
var daysDiff = Math.ceil(timeDiff / (1000 * 3600 * 24));
resultDiv.innerHTML = daysDiff + " days Post-Term";
return;
}
// Calculate the difference in milliseconds
var timeDiff = edd.getTime() – today.getTime();
// Convert milliseconds to days
var daysRemaining = Math.ceil(timeDiff / (1000 * 3600 * 24));
// Standard full term pregnancy is 40 weeks = 280 days
var fullTermDays = 280;
// Calculate gestational age in days
var gestationalAgeDays = fullTermDays – daysRemaining;
// Convert gestational age in days to weeks and days
var gestationalAgeWeeks = Math.floor(gestationalAgeDays / 7);
var gestationalAgeRemainingDays = gestationalAgeDays % 7;
if (gestationalAgeDays < 0) {
resultDiv.innerHTML = "Today's date is after the Due Date.";
} else {
resultDiv.innerHTML = gestationalAgeWeeks + " weeks and " + gestationalAgeRemainingDays + " days";
}
}