Key takeaways

A typical pregnancy lasts about 280 days or 40 weeks, and knowing the due date is crucial for planning prenatal care and preparing for potential preterm birth interventions.
Due dates can be calculated using the first day of the last menstrual period, the date of conception, or the date of embryo transfer in IVF, but they are estimates and not exact.
Ultrasounds can provide more precise information on gestational age, especially if done early, but due dates may still change based on health factors and the number of babies being carried.
While some may wish to plan their delivery around specific dates, due dates are primarily estimates, and actual delivery can vary, highlighting the importance of flexibility and regular prenatal care.

Due date calculator | How to calculate due date | Accuracy | Planning | How many weeks pregnant am I?

Congratulations! You’re pregnant, and now you’re looking forward to welcoming a baby in a few months. But now the question is…when, exactly, can you expect that little bundle of joy to arrive?

A typical pregnancy is approximately 280 days, or 40 weeks, according to Johns Hopkins Medicine. Of course, that can vary from woman to woman. A pregnancy is considered full term when you have reached the 39-week mark but haven’t hit the 41-week mark yet. Unless there are complicating factors, your obstetrician or nurse midwife will want you to hit that mark before delivering because it’s best for your baby. If it looks like your baby is going to be born early, you may need to undergo steroid injections to help make sure the baby’s lungs are ready.

“The frequency of adverse neonatal outcomes is lowest among uncomplicated pregnancies delivered between 39 0/7 weeks of gestation and 40 6/7 weeks of gestation,” the American College of Obstetricians and Gynecologists (ACOG) reports.

Plus, your due date (also called an estimated date of delivery or EDD) can help shape the prenatal care you receive. “The reason due dates are so important is because testing or treatment may need to be done at a certain gestation,” explains Judith Strunk, DNP, MSN, a family nurse practitioner and assistant professor for the Michigan State University College of Nursing. In other words, knowing your due date matters. Here’s how to figure yours out.

When is my due date?

Use this pregnancy due date calculator to get a better sense of when you can expect your little one to arrive.

Disclaimer: This pregnancy calculator assumes an average cycle of 28 days, with ovulation occurring on the 14th day after the beginning of the menstrual cycle. It does not account for inaccurate recall of the last menstrual period, irregularities in cycle length, or variability in the timing of ovulation.

How to calculate due date

“A due date is only as good as the information that you have going into it,” says Teresa Hoffman, MD, an OB-GYN with Hoffman and Associates, affiliated with The Family Childbirth and Children’s Center at Mercy Medical Center in Baltimore, Maryland.

That means that it’s definitely useful to have certain information when trying to calculate your due date if you want it to be reasonably accurate. And there are three different dates that you can use to calculate your estimated due date:

Your last menstrual period, which is determined by your first day of bleeding
The date you actually conceived
The day that your embryo transfer occurred if you’re using in vitro fertilization to conceive

Let’s look at each one of those dates in more detail.

Your last menstrual period

If you go this route, you’ll use the first day of your last menstrual period (lmp) as Day 1. You could essentially count forward until you reach Day 280, and that would be your due date. Or you could employ a three-step method known as Naegele’s Rule. You count backward three months from the date of your last menstrual period and then add seven days and one year. Pregnancy tests are most reliable starting the day of your missed period. By that point, you’d be about four weeks pregnant. But it’s important to note that Naegele’s rule is considered a guideline for the expected due date—it does not provide a definite date.

The date of conception

If you’re tracking your ovulation and you’re confident in the exact day that you got pregnant, you could calculate your due date from this date. Just count ahead 38 weeks, suggests the Cleveland Clinic. This assumes, however, that you know exactly when you ovulated and when you conceived.

Your IVF transfer date

During IVF, your provider will retrieve your eggs, create embryos, then transfer the embryos into your uterus. Day 1 will depend on how many days after your egg retrieval that the embryo transfer occurs on.

In other words, you may have a standard 28-day cycle, or you might not. You might ovulate exactly two weeks after the first day of your period, but you might not. And since your menstrual cycle may vary, that can affect your due date.

An ultrasound scan (or sonogram) can also provide some useful info and even shed a little more light on the gestational age. But the earlier that you get an ultrasound, the better, says Dr. Hoffman. That is, the closer to actual conception, the more accurate the ultrasound will be. “We usually do a sonogram at the first visit,” Dr. Hoffman says. “Usually we see people at seven, eight or nine weeks, or sometimes six weeks.”

How accurate is my due date? Can it change?

Just remember: Don’t get too attached to a specific due date. “Rarely do babies come on their due dates,” says Jessica Anderson, DNP, the director of midwifery services and associate professor with the University of Colorado Anschutz Medical Campus. “That’s rare. It happens, but it’s not the most common or likely thing that’s going to happen.”

Your due date is only an estimate. That is, you can get pretty close, but very few babies are actually born on their due dates. It is definitely possible, of course, says Dr. Hoffman, but there’s a lot of variability at work. “A due date is only as good as the information going into calculating it,” Strunk reiterates.

One reason why your due date may not match up with the date that you actually deliver: A textbook pregnancy might be 40 weeks, but not everyone delivers right on the 40-week mark. Some people deliver earlier, and some people deliver later.

Plus, 40 weeks is just the estimate for the end of a singleton pregnancy. Twin pregnancies tend to end sooner, with many twin deliveries occurring around the 36-week mark, according to Johns Hopkins Medicine. And triplets tend to arrive even sooner. The American Society for Reproductive Medicine suggests that 32 weeks is the average gestational age of triplets at the time of delivery.

Once you’re given a due date, could it change? Maybe, says Strunk. “It may change if there is more than a week discrepancy with a due date calculated from measurements taken during a first trimester ultrasound,” she says. Your due date may adjust, depending on factors such as how early you get an ultrasound and how many babies you’re carrying. (Dr. Hoffman says that first babies also tend to be born later.) So don’t get too attached to that due date until you have more information from your healthcare provider.

Can I plan my due date?

Some people are planners by nature, which extends to the desire to plan a pregnancy and delivery. They may want to aim for a delivery in a particular season or month, or they may want to avoid having a new baby at a particular time. For example, you may dread the idea of being pregnant during a long, hot summer. Or you might like to avoid having a baby during a month when many of your other family members already have birthdays. It’s a good idea to talk with your healthcare provider in advance if you have specific timelines for pregnancy and delivery.

As already noted, due dates are estimates. But you can give yourself a better chance at achieving a due date in your desired range by tracking your period to find out when you’re ovulating. Among other methods, some women opt to use ovulation predictor kits to detect luteinizing hormone in their urine. A rise in this hormone signals that ovulation is imminent. Once you have a good handle on your ovulatory time, you can plan sexual intercourse to coincide. And hopefully, you’ll get lucky.

But if not, don’t panic, especially if you’re just getting started with trying to get pregnant and you don’t have any complicating health issues that you’re aware of. “Sometimes it’s normal for it to take three to six or eight months to conceive,” Anderson says.

How many weeks pregnant am I?

As you probably know by now, pregnancy is counted in weeks, rather than months. (Except for the people who stop to pepper you with questions about your baby bump in the grocery store.)

Every pregnancy is divided into three equal parts called trimesters:

The first trimester is week 1 through the end of week 12
The second trimester is week 13 though the end of week 26
The third trimester is week 27 to the end of the pregnancy

You can probably expect certain milestones to occur during each trimester. For example, many women experience nausea and vomiting during the first trimester. Those symptoms fade for some women when the second trimester rolls around, and they start to feel a little more energetic. Second trimester is also when most women begin to notice little fluttery movements–signs that yes, there’s actually a baby in there. Your doctor may also perform an anatomy scan around 20 weeks of pregnancy during the second trimester, and you can find out your baby’s sex.

When the third trimester gets underway, your due date will probably loom large in your mind, as you may start the countdown toward delivery and meeting your new baby. Your provider will want to monitor you more closely as your due date approaches, in case any interventions need to happen. That due date will come in handy for making those types of decisions.