function calculatePregnancy() {
var lmpValue = document.getElementById("lmpDate").value;
var cycleValue = parseInt(document.getElementById("cycleLength").value);
if (!lmpValue) {
alert("Please select the first day of your last period.");
return;
}
var lmpDate = new Date(lmpValue);
var today = new Date();
// Adjust for cycle length (Standard is 28)
var cycleAdjustment = cycleValue – 28;
// Calculate time elapsed in milliseconds
var diffInMs = today.getTime() – lmpDate.getTime();
if (diffInMs < 0) {
alert("The date entered cannot be in the future.");
return;
}
// Calculations
var totalDays = Math.floor(diffInMs / (1000 * 60 * 60 * 24));
var weeks = Math.floor(totalDays / 7);
var days = totalDays % 7;
// Estimated Due Date (EDD): 280 days from LMP adjusted by cycle
var eddMs = lmpDate.getTime() + (280 * 24 * 60 * 60 * 1000) + (cycleAdjustment * 24 * 60 * 60 * 1000);
var eddDate = new Date(eddMs);
var options = { month: 'long', day: 'numeric', year: 'numeric' };
var eddFormatted = eddDate.toLocaleDateString(undefined, options);
// Remaining days
var remainingMs = eddMs – today.getTime();
var remainingDays = Math.max(0, Math.ceil(remainingMs / (1000 * 60 * 60 * 24)));
// Determine Trimester
var trimester = "";
if (weeks < 13) {
trimester = "First Trimester";
} else if (weeks < 27) {
trimester = "Second Trimester";
} else {
trimester = "Third Trimester";
}
// Display Results
document.getElementById("pregnancyResult").style.display = "block";
document.getElementById("currentWeekDisplay").innerText = "You are " + weeks + " weeks and " + days + " days pregnant!";
document.getElementById("dueDateDisplay").innerText = eddFormatted;
document.getElementById("trimesterDisplay").innerText = trimester;
document.getElementById("daysRemaining").innerText = remainingDays + " days to go";
}
How to Calculate Your Pregnancy Week by Week
Understanding where you are in your pregnancy journey is vital for tracking your baby's development and planning for your new arrival. While a healthcare professional provides the most accurate assessment, you can calculate your estimated progress using the "Last Menstrual Period" (LMP) method.
The Math Behind the Due Date
Most pregnancies last approximately 40 weeks (280 days) from the first day of your last menstrual period. This calculation follows Naegele's Rule, which assumes a standard 28-day menstrual cycle. If your cycle is longer or shorter than 28 days, our calculator adjusts the results to provide a more personalized estimate.
The Three Trimesters
A pregnancy is traditionally divided into three stages called trimesters:
First Trimester (Weeks 1-12): The period of rapid development where major organs begin to form.
Second Trimester (Weeks 13-26): Often called the "golden period," where the baby grows significantly and you may begin to feel movement.
Third Trimester (Weeks 27-40): The final stretch where the baby gains weight and prepares for birth.
Example Calculation
If the first day of your last period was January 1st and you have a 28-day cycle:
Add 280 days to January 1st.
Your Estimated Due Date (EDD) would be October 8th.
If today is February 12th, you would be 6 weeks and 0 days pregnant.
Disclaimer: This calculator is for informational purposes only. Only a medical professional can confirm your pregnancy and provide an official due date via ultrasound or clinical examination.