Pregnancy Due Date Calculator
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Pregnancy Due Date Calculator
Your Pregnancy Information:
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Understanding Pregnancy Dating
Calculating the gestational age of a pregnancy is crucial for monitoring fetal development, planning prenatal care, and estimating the due date. The most common method used by healthcare providers is based on the Last Menstrual Period (LMP). This method assumes a standard 28-day menstrual cycle with ovulation occurring around day 14.
The standard calculation for a full-term pregnancy is 40 weeks (280 days) from the first day of the LMP. This calculator uses this widely accepted Naegele's Rule to estimate your due date and current gestational age.
How the Calculation Works:
- Due Date Estimation (Naegele's Rule): Add 7 days to the first day of your LMP and then subtract 3 months, or add 9 months. For example, if your LMP started on October 1st, 2023:
- Add 7 days: October 8th, 2023
- Add 9 months: July 8th, 2024
- So, the estimated due date is July 8th, 2024.
- Gestational Age (Weeks): The number of weeks is calculated by determining the number of days between the LMP start date and the current date, and then dividing by 7. This calculator determines the weeks and days of pregnancy based on the LMP start date you provide.
Important Considerations:
- Irregular Cycles: This calculation is most accurate for individuals with regular 28-day cycles. If your cycles are significantly longer or shorter, or if you have irregular periods, the estimated due date and gestational age may be less precise.
- Ovulation Timing: Ovulation can vary. Some women may ovulate earlier or later than day 14, which can affect the actual conception date and thus the gestational age.
- Early Ultrasound: In cases of uncertainty or irregular cycles, an early ultrasound in the first trimester is often the most accurate method for dating a pregnancy.
- Consult Your Doctor: This calculator is for informational purposes only and should not replace professional medical advice. Always consult with your healthcare provider for accurate pregnancy dating and guidance.
By providing your LMP start date, you can get a quick estimate of your current pregnancy stage and your estimated due date.
function calculatePregnancyWeeks() {
var lmpDateInput = document.getElementById("lastPeriodStartDate");
var lmpDateStr = lmpDateInput.value;
if (!lmpDateStr) {
document.getElementById("pregnancyWeeks").textContent = "Please enter your LMP start date.";
document.getElementById("estimatedDueDate").textContent = "";
return;
}
var lmpDate = new Date(lmpDateStr);
var today = new Date();
// Check if the date is valid
if (isNaN(lmpDate.getTime())) {
document.getElementById("pregnancyWeeks").textContent = "Invalid date format.";
document.getElementById("estimatedDueDate").textContent = "";
return;
}
// Calculate estimated due date (Naegele's Rule: LMP + 7 days – 3 months OR LMP + 9 months)
var dueDate = new Date(lmpDate);
dueDate.setDate(lmpDate.getDate() + 7); // Add 7 days
dueDate.setMonth(lmpDate.getMonth() + 9); // Add 9 months
// Format the due date
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedDueDate = dueDate.toLocaleDateString(undefined, options);
// Calculate the difference in days between LMP and today
var timeDiff = today.getTime() – lmpDate.getTime();
var daysDiff = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
// Calculate weeks and days of pregnancy
var weeks = Math.floor(daysDiff / 7);
var remainingDays = daysDiff % 7;
var pregnancyWeeksText = weeks + " weeks and " + remainingDays + " days";
// Display results
document.getElementById("pregnancyWeeks").textContent = pregnancyWeeksText;
document.getElementById("estimatedDueDate").textContent = "Estimated Due Date: " + formattedDueDate;
}