Calculate your estimated due date and current pregnancy stage.
Estimated Due Date (EDD):
Current Pregnancy Progress:
Remaining Days:
Current Trimester:
Due Date Calculator Week by Week: Understanding Your Pregnancy Timeline
Finding out you are pregnant is one of the most exciting moments in life. The first question most parents-to-be ask is, "When is the baby coming?" Our due date calculator week by week provides an accurate estimate based on your biological cycle, helping you prepare for each milestone of your journey.
How the Due Date is Calculated
Most pregnancies last approximately 40 weeks (280 days) from the first day of the last menstrual period (LMP). While many believe pregnancy lasts exactly nine months, the medical community tracks it by weeks and trimesters to ensure precise monitoring of fetal development.
Naegele's Rule
Our calculator utilizes a modified version of Naegele's Rule. The basic formula is: LMP + 7 days – 3 months + 1 year. We also adjust for your specific cycle length. If your cycle is longer than the standard 28 days, your ovulation (and therefore conception) likely occurred later, which our tool accounts for to give you a more accurate date.
Pregnancy Milestones: Week by Week
Weeks 1-12 (First Trimester): This is the period of rapid development. The heart begins to beat, and major organs start forming. Most early pregnancy symptoms like morning sickness occur here.
Weeks 13-26 (Second Trimester): Often called the "honeymoon phase," energy levels usually return. This is when you'll likely feel the first kicks (quickening) and find out the baby's biological sex via ultrasound.
Weeks 27-40 (Third Trimester): The baby is growing rapidly and gaining weight. You may experience more physical discomfort as the due date approaches.
Is the Due Date Guaranteed?
It is important to remember that a due date is an estimate. In fact, only about 4% to 5% of babies are born exactly on their due date. Most babies arrive between 37 and 42 weeks. Factors such as maternal age, previous pregnancies, and the baby's health can influence the timing of labor.
Example Calculation
If your Last Menstrual Period was January 1st and you have a 28-day cycle:
Estimated Due Date: October 8th.
Conception Date: Approximately January 15th.
End of First Trimester: March 26th.
Tips for Using Your Results
Once you have your week-by-week timeline, use it to schedule your prenatal appointments. Your healthcare provider will use ultrasound measurements in the first trimester (the "dating scan") to confirm or adjust the date provided by this calculator, as ultrasound is often more accurate than LMP tracking.
function calculatePregnancy() {
var lmpInput = document.getElementById("lmpDate").value;
var cycleLength = parseInt(document.getElementById("cycleLength").value);
if (!lmpInput) {
alert("Please select the date of your last period.");
return;
}
var lmpDate = new Date(lmpInput);
var today = new Date();
// Standard EDD is LMP + 280 days.
// Adjust for cycle length: add (cycleLength – 28) days
var cycleAdjustment = cycleLength – 28;
var eddDate = new Date(lmpDate.getTime());
eddDate.setDate(eddDate.getDate() + 280 + cycleAdjustment);
// Calculate Current Status
var diffTime = Math.abs(today – lmpDate);
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
var weeks = Math.floor(diffDays / 7);
var days = diffDays % 7;
// Days left until due date
var timeLeft = eddDate – today;
var daysLeft = Math.ceil(timeLeft / (1000 * 60 * 60 * 24));
// Display results
document.getElementById("resultArea").style.display = "block";
document.getElementById("eddResult").innerText = eddDate.toDateString();
if (diffDays 300) {
document.getElementById("currentStatus").innerText = "Post-term / Delivered";
} else {
document.getElementById("currentStatus").innerText = weeks + " Weeks, " + days + " Days";
}
document.getElementById("daysLeft").innerText = daysLeft > 0 ? daysLeft : "0";
// Trimester Logic
var tri = "";
var milestoneText = "";
if (weeks < 13) {
tri = "First Trimester";
milestoneText = "Week " + weeks + " Milestone: Your baby is currently developing vital organs. In the first trimester, the neural tube (which becomes the brain and spinal cord) is forming. Make sure you are taking folic acid!";
} else if (weeks < 27) {
tri = "Second Trimester";
milestoneText = "Week " + weeks + " Milestone: You are in the 'Golden Period'. Your baby can now hear sounds and is starting to move more vigorously. Many parents perform their anatomy scan between weeks 18-22.";
} else {
tri = "Third Trimester";
milestoneText = "Week " + weeks + " Milestone: The home stretch! Your baby is gaining fat and practicing breathing. You may feel more pressure as the baby moves lower into the pelvis (dropping).";
}
document.getElementById("trimesterStatus").innerText = tri;
document.getElementById("milestoneInfo").innerHTML = milestoneText;
// Scroll to results on mobile
document.getElementById("resultArea").scrollIntoView({ behavior: 'smooth' });
}