Enter your dates to see baby's development status.
How Your Pregnancy Due Date is Calculated
Most pregnancies last approximately 40 weeks (280 days) from the first day of your last menstrual period (LMP). Our calculator uses Naegele's Rule, adjusted for your specific cycle length, to estimate your due date and current week of pregnancy.
Understanding Pregnancy Trimesters
First Trimester (Week 1 – Week 12): This is the period of rapid development where the embryo becomes a fetus and all major organs begin to form.
Second Trimester (Week 13 – Week 26): Often called the "golden period," morning sickness usually fades, and you may begin to feel the baby move (quickening).
Third Trimester (Week 27 – Week 40): The baby grows significantly in size and weight, preparing for life outside the womb.
Weekly Development Milestones
Tracking your pregnancy week by week allows you to visualize how your baby is growing. For example:
Week 8: Your baby is the size of a raspberry and has tiny webbed hands and feet.
Week 20: You are halfway there! The baby is the size of a banana and can swallow.
Week 32: The baby is the size of a squash and is practicing breathing by inhaling amniotic fluid.
Example Calculation
If your last period started on January 1st and you have a standard 28-day cycle, your estimated due date would be October 8th. By April 1st, you would be approximately 12 weeks and 6 days pregnant, marking the end of your first trimester.
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();
// Normalize cycle length adjustment (Naegele's rule assumes 28 days)
var cycleAdjustment = cycleLength – 28;
// Due Date = LMP + 280 days + cycle adjustment
var dueDate = new Date(lmpDate);
dueDate.setDate(dueDate.getDate() + 280 + cycleAdjustment);
// Calculate difference in time
var diffTime = today.getTime() – lmpDate.getTime();
var diffDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
if (diffDays 290) {
alert("Based on this date, the pregnancy would likely be completed. Please check your dates.");
}
var weeks = Math.floor(diffDays / 7);
var days = diffDays % 7;
// Calculate Days Remaining
var timeRemaining = dueDate.getTime() – today.getTime();
var daysRemaining = Math.ceil(timeRemaining / (1000 * 60 * 60 * 24));
if (daysRemaining < 0) daysRemaining = 0;
// Determine Trimester
var trimester = "";
if (weeks < 13) {
trimester = "First Trimester";
} else if (weeks < 27) {
trimester = "Second Trimester";
} else {
trimester = "Third Trimester";
}
// Milestone Logic
var milestone = "";
if (weeks < 4) {
milestone = "Your baby is currently a blastocyst, a tiny ball of cells smaller than a poppy seed.";
} else if (weeks < 8) {
milestone = "Baby's heart has started beating! They are roughly the size of a blueberry.";
} else if (weeks < 12) {
milestone = "Vital organs are forming. Your baby is the size of a lime and is starting to move, though you can't feel it yet.";
} else if (weeks < 16) {
milestone = "Baby can now make facial expressions and is about the size of an avocado.";
} else if (weeks < 20) {
milestone = "The baby's ears are developed and they can hear your voice. Size: Large mango.";
} else if (weeks < 24) {
milestone = "The baby's taste buds are developing. They are about the size of an ear of corn.";
} else if (weeks < 28) {
milestone = "Baby is opening their eyes and beginning to blink. Size: Large eggplant.";
} else if (weeks < 32) {
milestone = "The baby is gaining weight rapidly and has firm fingernails. Size: Squash.";
} else if (weeks < 36) {
milestone = "The baby is taking up most of the space in the uterus. Size: Papaya.";
} else {
milestone = "Your baby is full-term and ready to meet the world! Size: Watermelon.";
}
// Display Results
document.getElementById('resDueDate').innerHTML = dueDate.toDateString();
document.getElementById('resAge').innerHTML = weeks + " Weeks, " + days + " Days";
document.getElementById('resTrimester').innerHTML = trimester;
document.getElementById('resDaysLeft').innerHTML = daysRemaining + " Days";
document.getElementById('resMilestone').innerHTML = "Development Milestone: " + milestone;
document.getElementById('preg-result-box').style.display = 'block';
}