Congratulations on your pregnancy journey! Knowing your gestational age and estimated due date (EDD) is crucial for tracking your baby's development and preparing for their arrival. Our Pregnancy Week by Week Calculator helps you determine these key dates based on the first day of your last menstrual period (LMP).
How the Pregnancy Calculator Works
Most pregnancy calculators, including this one, use the "LMP method" to estimate your due date. This method assumes that conception occurred approximately two weeks after the start of your last period and that a full-term pregnancy lasts about 40 weeks (280 days) from your LMP. While the average menstrual cycle is 28 days, you can optionally input your typical cycle length. However, for standard medical dating, gestational age and EDD are primarily calculated from the LMP, assuming a 280-day pregnancy duration.
Last Menstrual Period (LMP): This is the first day of your last period. It's the most common starting point for pregnancy dating.
Gestational Age: This refers to how far along you are in your pregnancy, measured in weeks and days from your LMP to today's date.
Estimated Due Date (EDD): This is the approximate date your baby is expected to arrive, typically 40 weeks (280 days) from your LMP.
Why is Knowing Your Gestational Age Important?
Tracking your pregnancy week by week offers numerous benefits:
Monitoring Baby's Development: Each week brings new milestones for your baby's growth and organ development. Knowing your current week helps you understand what changes to expect.
Scheduling Appointments: Healthcare providers use your gestational age to schedule important prenatal tests, screenings, and ultrasounds at the appropriate times.
Preparing for Birth: As you approach your due date, you can better plan for labor, delivery, and the arrival of your newborn.
Understanding Your Body: Pregnancy brings many changes to your body. Knowing your current week can help you anticipate and understand common symptoms and experiences.
The Trimesters of Pregnancy
Pregnancy is typically divided into three trimesters, each with its own unique characteristics and developmental stages:
First Trimester (Weeks 1-13): This period begins with conception and is marked by rapid cell division and the formation of major organs. Many women experience morning sickness and fatigue during this time.
Second Trimester (Weeks 14-27): Often considered the "golden trimester," many early pregnancy symptoms subside, and you might start to feel your baby move. The baby grows significantly, and gender can often be determined.
Third Trimester (Weeks 28-40+): The final stretch! Your baby continues to grow and mature, gaining weight and preparing for birth. You might experience more discomfort as your body prepares for labor.
Important Considerations
While this calculator provides a good estimate, it's important to remember that:
Due dates are estimates: Only about 5% of babies are born exactly on their due date. Most arrive within a week or two before or after.
Medical confirmation: Always confirm your due date and gestational age with your healthcare provider. Ultrasounds, especially early in pregnancy, can provide a more accurate dating.
Irregular periods: If you have very irregular periods, dating your pregnancy based solely on LMP can be less accurate. Your doctor will likely use an early ultrasound for more precise dating.
Example Calculation
Let's say your Last Menstrual Period (LMP) started on January 15, 2024, and today's date is June 20, 2024.
The calculator would determine that you are approximately 22 weeks and 1 day pregnant.
Your Estimated Due Date (EDD) would be around October 22, 2024.
You would be in your Second Trimester.
You would have approximately 124 days remaining until your due date.
Use the calculator above to find your own personalized pregnancy details!
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function calculatePregnancy() {
var lmpDateStr = document.getElementById("lmpDate").value;
var cycleLength = parseInt(document.getElementById("cycleLength").value);
var resultDiv = document.getElementById("result");
if (!lmpDateStr) {
resultDiv.innerHTML = "Please enter the first day of your Last Menstrual Period.";
return;
}
var lmpDate = new Date(lmpDateStr + "T00:00:00"); // Parse as UTC to avoid timezone issues
var today = new Date();
today.setHours(0, 0, 0, 0); // Set today to start of day for consistent calculation
// Validate LMP date
if (isNaN(lmpDate.getTime())) {
resultDiv.innerHTML = "Invalid LMP date. Please use a valid date format.";
return;
}
// Ensure cycle length is a valid number, otherwise default to 28
if (isNaN(cycleLength) || cycleLength 45) {
cycleLength = 28;
}
// Calculate gestational age in days from LMP to today
var diffTime = today.getTime() – lmpDate.getTime();
var gestationalDays = Math.floor(diffTime / (1000 * 60 * 60 * 24));
if (gestationalDays = 0 && currentWeeks = 14 && currentWeeks = 28 && currentWeeks 42) {
trimester = "Post-term (beyond 42 weeks)";
} else {
trimester = "Not yet pregnant or invalid gestational age";
}
// Format EDD for display
var options = { year: 'numeric', month: 'long', day: 'numeric' };
var formattedEdd = eddDate.toLocaleDateString('en-US', options);
var output = "
Your Pregnancy Details:
";
output += "Current Gestational Age: " + currentWeeks + " weeks and " + currentDays + " days";
output += "Estimated Due Date (EDD): " + formattedEdd + "";
output += "Current Trimester: " + trimester + "";
if (daysRemaining >= 0) {
output += "Days Remaining Until Due Date: " + daysRemaining + " days";
} else {
output += "Days Past Due Date: " + Math.abs(daysRemaining) + " days";
}
var weekInfo = getWeekSpecificInfo(currentWeeks);
if (weekInfo) {
output += "This Week's Focus (" + currentWeeks + " weeks): " + weekInfo + "";
}
resultDiv.innerHTML = output;
}
function getWeekSpecificInfo(week) {
var info = {
"1": "Conception typically occurs around week 2, but pregnancy is counted from LMP. Your body is preparing.",
"2": "Fertilization usually happens this week. The fertilized egg begins its journey to the uterus.",
"3": "Implantation occurs! The blastocyst burrows into the uterine lining.",
"4": "The embryo is tiny, about the size of a poppy seed. The neural tube, which becomes the brain and spinal cord, starts to form.",
"5": "Your baby is now the size of a sesame seed. The heart begins to beat, and major organs start to develop.",
"6": "Your baby is about the size of a lentil. Facial features begin to emerge, and limb buds appear.",
"7": "Your baby is the size of a blueberry. The brain is developing rapidly, and tiny hands and feet are forming.",
"8": "Your baby is about the size of a kidney bean. Fingers and toes are becoming more distinct, and the eyes are forming.",
"9": "Your baby is the size of a grape. All major organs are in place, and the embryo is now called a fetus.",
"10": "Your baby is about the size of a kumquat. Essential organs are developing, and tiny teeth buds are forming.",
"11": "Your baby is the size of a fig. Fingers and toes are fully separated, and your baby can make tiny movements.",
"12": "Your baby is about the size of a lime. Reflexes are developing, and your baby can open and close its hands.",
"13": "Your baby is the size of a peach. The first trimester ends, and the risk of miscarriage significantly decreases.",
"14": "Your baby is about the size of a lemon. Hair is starting to grow, and your baby's kidneys are producing urine.",
"15": "Your baby is the size of an apple. Bones are hardening, and your baby can hear muffled sounds.",
"16": "Your baby is about the size of an avocado. Facial muscles are developing, allowing for expressions.",
"17": "Your baby is the size of a turnip. Fat stores are beginning to develop under the skin.",
"18": "Your baby is about the size of a bell pepper. You might start to feel your baby's first movements (quickening).",
"19": "Your baby is the size of a mango. Sensory development is booming, and nerve cells for senses are forming.",
"20": "Your baby is about the size of a banana. Halfway point! Your baby's skin is thickening, and hair is growing.",
"21": "Your baby is the size of a carrot. Your baby is becoming more active, and sleep-wake cycles are developing.",
"22": "Your baby is about the size of a papaya. Eyelids and eyebrows are fully formed, and your baby can hear clearly.",
"23": "Your baby is the size of a large grapefruit. Lungs are developing, and your baby is gaining weight.",
"24": "Your baby is about the size of a cantaloupe. Your baby's brain is growing rapidly, and taste buds are forming.",
"25": "Your baby is the size of a rutabaga. Your baby is gaining more fat, making their skin smoother.",
"26": "Your baby is about the size of a head of lettuce. Lungs are continuing to mature, and your baby can respond to sounds.",
"27": "Your baby is the size of a cauliflower. The third trimester is approaching, and your baby is practicing breathing.",
"28": "Your baby is about the size of an eggplant. Your baby's eyes can open and close, and they are developing sleep patterns.",
"29": "Your baby is the size of a butternut squash. Your baby is gaining weight rapidly and developing more fat layers.",
"30": "Your baby is about the size of a cabbage. Your baby's brain is developing rapidly, and they are storing iron.",
"31": "Your baby is the size of a coconut. Your baby's lungs are nearly mature, and they are practicing breathing movements.",
"32": "Your baby is about the size of a jicama. Your baby is gaining about half a pound a week and filling out.",
"33": "Your baby is the size of a pineapple. Bones are hardening, but the skull remains soft for birth.",
"34": "Your baby is about the size of a cantaloupe. Your baby's central nervous system is maturing, and they are gaining fat.",
"35": "Your baby is the size of a honeydew melon. Your baby is getting ready for birth, and organs are fully developed.",
"36": "Your baby is about the size of a romaine lettuce. Your baby is dropping lower into your pelvis (lightening).",
"37": "Your baby is considered full-term! Your baby is ready for birth, and lungs are fully mature.",
"38": "Your baby is about the size of a pumpkin. Your baby is continuing to gain weight and shed lanugo (fine hair).",
"39": "Your baby is the size of a small watermelon. Your baby is ready to meet you! The vernix caseosa (waxy coating) is thickening.",
"40": "Your baby is about the size of a large pumpkin. Your due date! Your baby is fully developed and waiting for labor to begin.",
"41": "Your baby is still growing and preparing. Your doctor may discuss induction options.",
"42": "Your baby is post-term. Medical induction is often recommended to ensure safety."
};
return info[week.toString()] || "No specific information available for this week yet. Consult your healthcare provider for personalized advice.";
}