Calculating your pregnancy due date is a crucial step in tracking your baby's development and preparing for birth. The most common method used by healthcare professionals is the Naegele's Rule, which estimates the due date based on the first day of your Last Menstrual Period (LMP). This calculator provides an estimated due date (EDD) and can also help you understand your current gestational age.
How the Calculation Works:
The standard human gestation period is approximately 40 weeks (or 280 days) from the first day of your last menstrual period.
Naegele's Rule: This rule adds 7 days to the first day of your LMP and then subtracts 3 months, followed by adding 1 year. For example, if your LMP started on July 10, 2023, you would add 7 days to get July 17, 2023, subtract 3 months to get April 17, 2023, and add 1 year to arrive at April 17, 2024.
Gestational Age: Gestational age is measured in weeks and days from the first day of your LMP. A typical full-term pregnancy is considered 37 to 40 weeks. This calculator allows you to input your current estimated gestational age to see how far along you are and what your EDD would be based on that.
Accuracy: While Naegele's Rule is widely used, it's an estimation. Ovulation and conception can vary, and not all pregnancies are exactly 40 weeks. Early ultrasound scans are often considered more accurate for determining gestational age, especially if your menstrual cycles are irregular.
Why Use This Calculator?
Early Preparation: Helps you anticipate key milestones and prepare for your baby's arrival.
Understanding Trimesters: Gives you a clearer picture of which trimester you are in.
Tracking Development: Allows you to follow along with typical fetal development stages week by week.
Information for Healthcare Providers: Provides a consistent reference point for discussions with your doctor or midwife.
Disclaimer: This calculator is for informational purposes only and should not replace professional medical advice. Always consult with your healthcare provider for accurate dating of your pregnancy and any health concerns.
function calculateDueDate() {
var lmpDateInput = document.getElementById("lmpDate");
var gestationalAgeWeeksInput = document.getElementById("gestationalAgeWeeks");
var gestationalAgeDaysInput = document.getElementById("gestationalAgeDays");
var lmpDateValue = lmpDateInput.value;
var gestationalAgeWeeksValue = parseInt(gestationalAgeWeeksInput.value);
var gestationalAgeDaysValue = parseInt(gestationalAgeDaysInput.value);
var dueDateResult = document.getElementById("dueDateResult");
var gestationalAgeResult = document.getElementById("gestationalAgeResult");
if (!lmpDateValue && (isNaN(gestationalAgeWeeksValue) || isNaN(gestationalAgeDaysValue))) {
dueDateResult.textContent = "Please enter LMP date or Gestational Age.";
gestationalAgeResult.textContent = "Gestational Age: -";
return;
}
var edd = null;
var currentGestationalAge = null;
if (lmpDateValue) {
var lmpDate = new Date(lmpDateValue);
var eddDate = new Date(lmpDate);
eddDate.setDate(lmpDate.getDate() + 7); // Add 7 days
eddDate.setMonth(lmpDate.getMonth() – 3); // Subtract 3 months
eddDate.setFullYear(lmpDate.getFullYear() + 1); // Add 1 year
edd = eddDate;
// Calculate current gestational age from LMP
var today = new Date();
var diffTime = today.getTime() – lmpDate.getTime();
var totalDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
// Ensure LMP date is in the past or today for age calculation
if (totalDays < 0) {
currentGestationalAge = "LMP date must be in the past or today.";
} else {
var weeks = Math.floor(totalDays / 7);
var days = totalDays % 7;
currentGestationalAge = weeks + " weeks and " + days + " days";
}
} else if (!isNaN(gestationalAgeWeeksValue) && !isNaN(gestationalAgeDaysValue)) {
if (gestationalAgeWeeksValue < 0 || gestationalAgeDaysValue 6) {
dueDateResult.textContent = "Invalid Gestational Age values.";
gestationalAgeResult.textContent = "Gestational Age: -";
return;
}
var totalWeeksToEDD = 40 – gestationalAgeWeeksValue;
var totalDaysToEDD = 7 – gestationalAgeDaysValue;
if (totalDaysToEDD >= 7) {
totalWeeksToEDD += Math.floor(totalDaysToEDD / 7);
totalDaysToEDD = totalDaysToEDD % 7;
}
var eddDate = new Date(); // Use today's date as the reference
eddDate.setDate(eddDate.getDate() + (totalWeeksToEDD * 7) + totalDaysToEDD);
edd = eddDate;
currentGestationalAge = gestationalAgeWeeksValue + " weeks and " + gestationalAgeDaysValue + " days";
}
if (edd) {
var options = { year: 'numeric', month: 'long', day: 'numeric' };
dueDateResult.textContent = edd.toLocaleDateString('en-US', options);
} else {
dueDateResult.textContent = "Calculation Error";
}
if (currentGestationalAge) {
gestationalAgeResult.textContent = "Current Gestational Age: " + currentGestationalAge;
} else {
gestationalAgeResult.textContent = "Gestational Age: -";
}
}