Pregnancy Week Calculator
Use this calculator to estimate your current pregnancy week and day, as well as your estimated due date (EDD) or last menstrual period (LMP) based on the information you provide.
Understanding Pregnancy Weeks
Calculating pregnancy weeks is a fundamental aspect of prenatal care, helping both expectant parents and healthcare providers track the baby's development and plan for important milestones. A full-term pregnancy typically lasts about 40 weeks, counted from the first day of the last menstrual period (LMP).
How Pregnancy Weeks Are Calculated
There are two primary methods for calculating pregnancy weeks:
-
Last Menstrual Period (LMP): This is the most common method. Pregnancy is traditionally counted from the first day of your last menstrual period, even though conception usually occurs about two weeks later. This method assumes a regular 28-day menstrual cycle with ovulation occurring around day 14. By adding 280 days (40 weeks) to your LMP date, an Estimated Due Date (EDD) can be determined.
-
Estimated Due Date (EDD): If you already have an EDD provided by your doctor, often confirmed by an early ultrasound, this date can be used to work backward and determine your current pregnancy week and even your estimated LMP.
Why Is It Important to Know Your Pregnancy Week?
- Tracking Fetal Development: Each week of pregnancy brings new developmental milestones for the baby. Knowing your current week helps you understand what changes to expect and what your baby is doing inside.
- Scheduling Appointments: Healthcare providers use your pregnancy week to schedule important screenings, tests, and ultrasounds at the appropriate times.
- Preparing for Birth: As you approach your due date, knowing your exact week helps you and your medical team prepare for labor and delivery.
- Personal Planning: It helps expectant parents plan for maternity leave, baby showers, and other preparations.
Example Calculation:
Let's say your Last Menstrual Period (LMP) started on January 1, 2024. To calculate your current pregnancy week:
- If today's date is April 15, 2024:
- The total number of days from January 1 to April 15 is 105 days.
- Dividing 105 days by 7 gives you 15 weeks.
- So, you would be approximately 15 weeks and 0 days pregnant.
- Your Estimated Due Date (EDD) would be around October 8, 2024 (January 1, 2024 + 280 days).
If your doctor gave you an Estimated Due Date (EDD) of October 8, 2024, and today is April 15, 2024:
- The total pregnancy duration is 280 days.
- Days remaining until EDD (October 8, 2024 – April 15, 2024) is 176 days.
- Days completed in pregnancy = 280 – 176 = 104 days.
- Dividing 104 days by 7 gives you 14 weeks and 6 days.
- So, you would be approximately 14 weeks and 6 days pregnant.
- Your estimated LMP would be around January 1, 2024 (October 8, 2024 – 280 days).
This calculator provides an estimate. Always consult with your healthcare provider for precise dating and medical advice regarding your pregnancy.
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function calculatePregnancyWeeks() {
var lmpDateInput = document.getElementById("lmpDate").value;
var eddDateInput = document.getElementById("eddDate").value;
var resultOutput = document.getElementById("resultOutput");
resultOutput.innerHTML = ""; // Clear previous results
var today = new Date();
today.setHours(0, 0, 0, 0); // Normalize today's date to start of day
var lmpDate, eddDate;
var hasLMP = false;
var hasEDD = false;
if (lmpDateInput) {
lmpDate = new Date(lmpDateInput);
lmpDate.setHours(0, 0, 0, 0);
if (!isNaN(lmpDate.getTime())) {
hasLMP = true;
}
}
if (eddDateInput) {
eddDate = new Date(eddDateInput);
eddDate.setHours(0, 0, 0, 0);
if (!isNaN(eddDate.getTime())) {
hasEDD = true;
}
}
if (!hasLMP && !hasEDD) {
resultOutput.innerHTML = "Please enter either your Last Menstrual Period (LMP) date or your Estimated Due Date (EDD).";
return;
}
var currentWeeks, currentDays;
var calculatedEDD, calculatedLMP;
if (hasLMP) {
// Calculate from LMP
var diffTime = today.getTime() – lmpDate.getTime();
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
if (diffDays < 0) {
resultOutput.innerHTML = "LMP date cannot be in the future. Please check your input.";
return;
}
currentWeeks = Math.floor(diffDays / 7);
currentDays = diffDays % 7;
calculatedEDD = new Date(lmpDate.getTime() + (280 * 24 * 60 * 60 * 1000)); // 280 days = 40 weeks
resultOutput.innerHTML =
"Based on your LMP of
" + lmpDate.toDateString() + ":" +
"You are approximately
" + currentWeeks + " weeks and " + currentDays + " days pregnant." +
"Your Estimated Due Date (EDD) is
" + calculatedEDD.toDateString() + ".";
} else if (hasEDD) {
// Calculate from EDD
var totalPregnancyDays = 280; // Standard 40 weeks
var daysUntilEDD = Math.floor((eddDate.getTime() – today.getTime()) / (1000 * 60 * 60 * 24));
if (daysUntilEDD > totalPregnancyDays) {
resultOutput.innerHTML = "EDD is too far in the future. Please check your input.";
return;
}
if (daysUntilEDD < -100) { // Allow for a few weeks past due date
resultOutput.innerHTML = "EDD is too far in the past. Please check your input.";
return;
}
var daysCompleted = totalPregnancyDays – daysUntilEDD;
currentWeeks = Math.floor(daysCompleted / 7);
currentDays = daysCompleted % 7;
calculatedLMP = new Date(eddDate.getTime() – (280 * 24 * 60 * 60 * 1000));
resultOutput.innerHTML =
"Based on your EDD of
" + eddDate.toDateString() + ":" +
"You are approximately
" + currentWeeks + " weeks and " + currentDays + " days pregnant." +
"Your Estimated Last Menstrual Period (LMP) was
" + calculatedLMP.toDateString() + ".";
}
}
function clearForm() {
document.getElementById("lmpDate").value = "";
document.getElementById("eddDate").value = "";
document.getElementById("resultOutput").innerHTML = "";
}