Pregnancy is typically calculated from the first day of your last menstrual period (LMP). This method is used because it's often the earliest date that can be accurately recalled. The standard full-term pregnancy is considered to be 40 weeks from your LMP.
This calculator helps you determine your estimated gestational age in weeks and months, and your expected due date based on your LMP and the current date.
How the Calculation Works:
Weeks of Pregnancy: The calculator determines the number of days between your LMP and the current date, then divides that by 7 to get the total number of weeks.
Months of Pregnancy: While pregnancy is often discussed in months, the medical standard is 40 weeks. To convert weeks to months, we use an average of 4.33 weeks per month (52 weeks / 12 months). Therefore, the displayed 'months pregnant' is an approximation.
Estimated Due Date (EDD): The EDD is calculated by adding 40 weeks (280 days) to the first day of your LMP. This is an estimate, and actual birth dates can vary.
Key Terms:
Last Menstrual Period (LMP): The first day of your most recent period. This is the standard starting point for calculating pregnancy duration.
Gestational Age: The age of the pregnancy, measured in weeks and days from the LMP.
Trimesters: Pregnancy is divided into three trimesters:
First Trimester: LMP to week 13
Second Trimester: Week 14 to week 27
Third Trimester: Week 28 to birth
Full Term: Typically considered between 37 and 40 weeks of gestation.
Disclaimer: 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.
function calculatePregnancy() {
var lmpInput = document.getElementById("lastMenstrualPeriod");
var currentDateInput = document.getElementById("currentDate");
var weeksPregnantDisplay = document.getElementById("weeksPregnant");
var monthsPregnantDisplay = document.getElementById("monthsPregnant");
var estimatedDueDateDisplay = document.getElementById("estimatedDueDate");
var lmpDate = new Date(lmpInput.value);
var currentDate = new Date(currentDateInput.value);
// Clear previous results
weeksPregnantDisplay.innerText = "";
monthsPregnantDisplay.innerText = "";
estimatedDueDateDisplay.innerText = "";
// Validate dates
if (isNaN(lmpDate.getTime()) || isNaN(currentDate.getTime())) {
alert("Please enter valid dates for both Last Menstrual Period and Today's Date.");
return;
}
if (currentDate = 3 ? " months" : " months"); // Simple approximation
if (weeks = 37) {
displayMonths = "Full Term (approx. 9+ months)";
} else {
displayMonths = Math.floor(weeks / 4) + " months";
if (weeks % 4 !== 0) {
displayMonths += ", " + (weeks % 4) + " weeks";
}
displayMonths += " pregnant";
}
monthsPregnantDisplay.innerText = "Approximate Gestational Age: " + displayMonths;
estimatedDueDateDisplay.innerText = "Estimated Due Date: " + formattedEdd;
}