Use this calculator to determine your current week of pregnancy, your estimated due date, and how many weeks you have left until your baby arrives. This calculation is based on the first day of your last menstrual period (LMP), which is the standard method used by healthcare professionals.
Understanding Your Pregnancy Weeks
Pregnancy is a remarkable journey, typically lasting around 40 weeks from the first day of your last menstrual period (LMP). While conception usually occurs about two weeks after your LMP, medical professionals count pregnancy from this earlier date because it's often the most reliable and easily identifiable starting point.
How is Pregnancy Calculated?
Our calculator uses the standard method: counting forward from your LMP. Here's what the results mean:
Current Pregnancy Week and Day: This tells you exactly how far along you are in your pregnancy. For example, "8 weeks and 3 days" means you are in your 9th week of pregnancy, having completed 8 full weeks and 3 days of the 9th week.
Estimated Due Date (EDD): This is the approximate date your baby is expected to arrive. It's calculated by adding 280 days (40 weeks) to your LMP. Keep in mind that only about 5% of babies are born exactly on their due date; most arrive within a week or two before or after.
Weeks and Days Remaining: This gives you an idea of how much time is left until your estimated due date, helping you plan and prepare for your baby's arrival.
Why is Knowing Your Pregnancy Week Important?
Knowing your exact week of pregnancy is crucial for several reasons:
Tracking Fetal Development: Each week brings new milestones in your baby's growth and development. Knowing your week helps you understand what changes to expect and what's happening inside your womb.
Antenatal Care: Healthcare providers use your pregnancy week to schedule important appointments, screenings, and tests at the appropriate times.
Personal Preparation: It helps you plan for maternity leave, prepare your home, and organize baby essentials.
Emotional Connection: Understanding your progress can help you feel more connected to your pregnancy journey and anticipate upcoming changes.
Factors Affecting Accuracy
While the LMP method is widely used, its accuracy depends on a few factors:
Regular Menstrual Cycles: This method is most accurate for individuals with regular 28-day cycles.
Recalling LMP: An accurate recollection of the first day of your LMP is essential.
Ultrasound Confirmation: Early ultrasounds (typically between 8-12 weeks) can provide a more precise estimated due date, especially if your cycles are irregular or you're unsure of your LMP.
Example Calculation:
Let's say your Last Menstrual Period (LMP) started on January 1, 2024.
If today's date is March 1, 2024:
Days since LMP: 60 days
Current Pregnancy: 8 weeks and 4 days
Estimated Due Date: October 8, 2024
Weeks Remaining: Approximately 31 weeks and 3 days
If today's date is July 15, 2024:
Days since LMP: 196 days
Current Pregnancy: 28 weeks and 0 days
Estimated Due Date: October 8, 2024
Weeks Remaining: Approximately 12 weeks and 0 days
This calculator provides a helpful estimate, but always consult with your healthcare provider for personalized medical advice and confirmation of your pregnancy timeline.
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function calculatePregnancyWeeks() {
var lmpDateString = document.getElementById("lastMenstrualPeriodDate").value;
var resultDiv = document.getElementById("pregnancyResult");
resultDiv.innerHTML = ""; // Clear previous results
if (!lmpDateString) {
resultDiv.innerHTML = "Please enter the first day of your Last Menstrual Period.";
return;
}
var lmpDate = new Date(lmpDateString);
// Check for invalid date input
if (isNaN(lmpDate.getTime())) {
resultDiv.innerHTML = "Invalid date entered. Please use a valid date format.";
return;
}
var today = new Date();
today.setHours(0, 0, 0, 0); // Normalize today's date to start of day
// Calculate difference in milliseconds
var timeDiff = today.getTime() – lmpDate.getTime();
// Convert to days
var daysSinceLMP = Math.floor(timeDiff / (1000 * 60 * 60 * 24));
if (daysSinceLMP < 0) {
resultDiv.innerHTML = "The LMP date cannot be in the future. Please enter a past or current date.";
return;
}
// Calculate current pregnancy week and day
var currentWeek = Math.floor(daysSinceLMP / 7);
var currentDay = daysSinceLMP % 7;
// Calculate Estimated Due Date (EDD) – 280 days (40 weeks) from LMP
var eddDate = new Date(lmpDate.getTime());
eddDate.setDate(lmpDate.getDate() + 280);
// Calculate remaining weeks and days
var totalPregnancyDays = 280;
var remainingDays = totalPregnancyDays – daysSinceLMP;
var remainingWeeks = Math.floor(remainingDays / 7);
var remainingDaysInWeek = remainingDays % 7;
// Format EDD for display
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedEdd = eddDate.toLocaleDateString('en-US', options);
var resultsHtml = "
Your Pregnancy Details:
";
resultsHtml += "Current Pregnancy: " + currentWeek + " weeks and " + currentDay + " days";
resultsHtml += "Estimated Due Date (EDD): " + formattedEdd + "";
if (remainingDays > 0) {
resultsHtml += "Weeks Remaining Until EDD: " + remainingWeeks + " weeks and " + remainingDaysInWeek + " days";
} else if (remainingDays === 0) {
resultsHtml += "Estimated Due Date is Today!";
} else {
resultsHtml += "Your Estimated Due Date was: " + formattedEdd + " (" + Math.abs(remainingWeeks) + " weeks and " + Math.abs(remainingDaysInWeek) + " days ago)";
}
resultDiv.innerHTML = resultsHtml;
}
// Set default LMP date to 10 weeks ago for demonstration
window.onload = function() {
var today = new Date();
var defaultLMP = new Date(today.getTime() – (10 * 7 * 24 * 60 * 60 * 1000)); // 10 weeks ago
var year = defaultLMP.getFullYear();
var month = (defaultLMP.getMonth() + 1).toString().padStart(2, '0');
var day = defaultLMP.getDate().toString().padStart(2, '0');
document.getElementById("lastMenstrualPeriodDate").value = year + '-' + month + '-' + day;
calculatePregnancyWeeks(); // Run calculation on load with default value
};