Use this calculator to estimate your current pregnancy week and your estimated due date based on the first day of your last menstrual period (LMP).
Results:
function calculatePregnancyWeeks() {
var lmpDateStr = document.getElementById("lmpDate").value;
var currentDateStr = document.getElementById("currentDate").value;
var lmp = new Date(lmpDateStr);
var current = new Date(currentDateStr);
var pregnancyWeeksResultDiv = document.getElementById("pregnancyWeeksResult");
var estimatedDueDateResultDiv = document.getElementById("estimatedDueDateResult");
// Clear previous results
pregnancyWeeksResultDiv.innerHTML = "";
estimatedDueDateResultDiv.innerHTML = "";
// Validate inputs
if (isNaN(lmp.getTime()) || isNaN(current.getTime())) {
pregnancyWeeksResultDiv.innerHTML = "Please enter valid dates for both fields.";
return;
}
if (current.getTime() < lmp.getTime()) {
pregnancyWeeksResultDiv.innerHTML = "Today's Date cannot be earlier than the First Day of Last Menstrual Period.";
return;
}
// Calculate difference in milliseconds
var diffMs = current.getTime() – lmp.getTime();
// Convert milliseconds to days
var diffDays = Math.floor(diffMs / (1000 * 60 * 60 * 24));
// Calculate weeks and remaining days
var weeks = Math.floor(diffDays / 7);
var days = diffDays % 7;
// Calculate estimated due date (LMP + 280 days)
var dueDateMs = lmp.getTime() + (280 * 24 * 60 * 60 * 1000);
var estimatedDueDate = new Date(dueDateMs);
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedDueDate = estimatedDueDate.toLocaleDateString('en-US', options);
pregnancyWeeksResultDiv.innerHTML = "You are approximately " + weeks + " weeks and " + days + " days pregnant.";
estimatedDueDateResultDiv.innerHTML = "Your estimated due date is: " + formattedDueDate + ".";
}
// Set default current date to today
document.addEventListener('DOMContentLoaded', function() {
var today = new Date();
var dd = String(today.getDate()).padStart(2, '0');
var mm = String(today.getMonth() + 1).padStart(2, '0'); //January is 0!
var yyyy = today.getFullYear();
document.getElementById('currentDate').value = yyyy + '-' + mm + '-' + dd;
});
.pregnancy-weeks-calculator-container {
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
background-color: #f9f9f9;
padding: 25px;
border-radius: 10px;
box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
max-width: 600px;
margin: 30px auto;
border: 1px solid #e0e0e0;
}
.pregnancy-weeks-calculator-container h2 {
color: #333;
text-align: center;
margin-bottom: 20px;
font-size: 1.8em;
}
.pregnancy-weeks-calculator-container p {
color: #555;
text-align: center;
margin-bottom: 25px;
line-height: 1.6;
}
.calculator-form label {
display: block;
margin-bottom: 8px;
color: #444;
font-weight: bold;
font-size: 0.95em;
}
.calculator-form input[type="date"] {
width: calc(100% – 22px);
padding: 12px;
margin-bottom: 20px;
border: 1px solid #ccc;
border-radius: 6px;
font-size: 1em;
box-sizing: border-box;
}
.calculator-form button {
background-color: #4CAF50;
color: white;
padding: 14px 25px;
border: none;
border-radius: 6px;
cursor: pointer;
font-size: 1.1em;
width: 100%;
transition: background-color 0.3s ease;
box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
}
.calculator-form button:hover {
background-color: #45a049;
}
.calculator-results {
margin-top: 30px;
padding-top: 20px;
border-top: 1px solid #eee;
}
.calculator-results h3 {
color: #333;
text-align: center;
margin-bottom: 15px;
font-size: 1.5em;
}
.result-output {
background-color: #e8f5e9;
color: #2e7d32;
padding: 15px;
border-radius: 8px;
margin-bottom: 15px;
text-align: center;
font-size: 1.1em;
font-weight: bold;
border: 1px solid #c8e6c9;
}
.result-output:empty {
display: none;
}
Understanding Pregnancy Weeks and Due Dates
Calculating pregnancy weeks is a fundamental aspect of prenatal care, helping expectant parents and healthcare providers track the baby's development and plan for important milestones. Unlike common belief, pregnancy is not counted from the moment of conception, which can be difficult to pinpoint. Instead, it's traditionally measured from the first day of the Last Menstrual Period (LMP).
Why Calculate from LMP?
The first day of your LMP is used as the starting point because it's usually the most reliable and easily identifiable date for most women. While conception typically occurs about two weeks after the LMP (around ovulation), counting from LMP provides a consistent 40-week timeline for a full-term pregnancy. This method helps standardize gestational age calculations across medical practices.
How the Calculation Works
Our Pregnancy Weeks Calculator uses a straightforward method:
First Day of Last Menstrual Period (LMP): This is the crucial starting point.
Today's Date (or Date to Calculate For): This is the date for which you want to know your current pregnancy week.
Difference in Days: The calculator determines the total number of days between your LMP and the specified current date.
Conversion to Weeks and Days: This total number of days is then divided by seven to give you the number of full weeks, with any remainder indicating additional days.
For example, if your LMP was January 1, 2023, and today is April 10, 2023, the calculator would determine that 99 days have passed. Dividing 99 by 7 gives you 14 with a remainder of 1. This means you are approximately 14 weeks and 1 day pregnant.
Estimating Your Due Date
The estimated due date (EDD) is also derived from your LMP. The standard calculation adds 280 days (or 40 weeks) to the first day of your LMP. This is often referred to as Naegele's Rule. While this provides a good estimate, it's important to remember that only about 5% of babies are born exactly on their due date. Most babies arrive between 37 and 42 weeks of gestation.
Importance of Knowing Your Pregnancy Weeks
Prenatal Appointments: Healthcare providers use gestational age to schedule ultrasounds, screenings, and other vital tests at appropriate times.
Fetal Development Tracking: Knowing the week helps you understand what developmental milestones your baby is reaching.
Planning and Preparation: It assists in planning for maternity leave, preparing the nursery, and attending childbirth classes.
Medical Decisions: In some cases, gestational age can influence medical decisions regarding interventions or delivery timing.
Factors That Can Affect Accuracy
While the LMP method is widely used, its accuracy can be affected by:
Irregular Menstrual Cycles: If your cycles are not consistently 28 days long, your ovulation might occur earlier or later than the typical two-week mark, making the LMP-based due date less precise.
Uncertain LMP: If you can't recall the exact date of your LMP, or if you conceived while on birth control, an early ultrasound will be more accurate for dating the pregnancy.
Always consult with your healthcare provider for the most accurate dating of your pregnancy and personalized medical advice. This calculator provides a helpful estimate for informational purposes.