What Does Your Due Date Actually Mean?

You may be surprised to learn the average week that first-time parents give birth. Here's why the term "due date" is a bit of a misnomer and what it means for your pregnancy.

Friendly OBGYN gently presses on pregnant woman's abdominal. She is checking the fetal position. The pregnant woman is in her third trimester.

Getty Images / A boy and the sea

Pregnancy due dates can be tricky things: On one hand, they're an exciting milestone that many pregnant people are eager to reach. On the other, they can quickly become a misleading "deadline" that may cause more stress and confusion than excitement.

Doctors call due dates EDDs (which stands for "estimated delivery date") for good reason: They're just an estimate that can be off by as much as two weeks, explains the American College of Obstetricians and Gynecologists (ACOG).

Read on to learn about the accuracy of due dates, plus the timeframe when first-time parents actually give birth.

What Is a Due Date?

In pregnancy, a due date is a calculation that estimates when the pregnant person is expected to give birth, barring any complications or interventions. Health care providers use this date to help monitor fetal growth and schedule exams. Due dates are simply an estimate, and the date that a person actually gives birth is influenced by a number of factors.

How Accurate Are Due Dates?

Very few people give birth on their actual due date. Indeed, research shows that only about 4% of people deliver on their due date, while 70% deliver within 10 days of it. The good news is that while you may not give birth exactly on your due date, your chances of having a full-term baby are good, barring any medical complications.

According to data from the Centers for Disease Control and Prevention (CDC), the majority of babies in the U.S. are born full-term. Just over 10% of babies are born preterm, which means before 37 weeks. Very few babies are born "late-term," which ACOG defines as over 42 weeks of pregnancy.

How Due Dates Are Calculated

ACOG explains that traditionally, due dates have been calculated by adding nine months and seven days (or 280 days) to the first day of the pregnant person's last menstrual period (LMP). This calculation assumes that the person ovulated two weeks after getting their last period, or on day 14 of their cycle.

While it's widely used, this method is not extremely accurate and doesn't account for things like menstrual cycle irregularities, unpredictable ovulation, how long implantation can take, and of course, human error.

Pregnant people might also calculate their baby's predicted arrival using their conception date; it'll be about 266 days (38 weeks) after this. Again, this method is not completely accurate, especially since many people don't know when they conceived.

When the date of conception is known, such as with in vitro fertilization (IVF), the estimated due date can be calculated by adding 266 days to that date, rather than the first day of the LMP. This estimated due date will typically be a lot more accurate than a due date calculated using the LMP or conception date.

ACOG considers a first-trimester ultrasound (up to right before 14 weeks of gestation) to be the most accurate way to predict a pregnant person's due date, especially if LMP or conception date isn't known. In fact, if you get a first-trimester ultrasound, your doctor may adjust your initial due date depending on what the ultrasound shows.

A South African study found that people who used both their last menstrual date and a smartphone app to track their cycles were able to predict their due dates more accurately than those who used just their period date alone. Talk to your doctor about using any cycle data you have to help predict your due date.

You can also use our due date calculator here.

The Average Week First-Time Parents Give Birth

Wondering the average week of pregnancy that first-time parents give birth? Research suggests that about half of people giving birth for the first time deliver by 40 weeks and five days. This finding suggests that when left to go into labor without intervention, first-time pregnancies often last longer than the 40-week estimate used when calculating due dates.

Other research highlights the variability of birth dates compared to estimated due dates. One study found that 66% of pregnant people gave birth within seven days of their estimated due dates. And the more recent study of 325 birthing people out of South Africa found that 88.3% of people delivered within two weeks of their due dates.

That said, these averages have little influence on when an individual will deliver, because many factors go into determining when a baby is born, including medical interventions like inductions and planned C-sections.

How to Get Through the Last Weeks of Pregnancy


While you count down the long weeks and months to your due date, you may experience some frustration, which is very normal. It's not always easy to get through those last weeks of pregnancy, especially if your due date has come and gone and you're incredibly anxious to deliver.

Getting through those last weeks is as much a mental game as it is a physical one, and how you think about your due date may help. Consider the following scenarios.

Two friends are both due at the end of August. Both are first-timers with uncomplicated, healthy pregnancies. They're both eager to meet their babies, but one is counting down the days to their due date like they're going on a cruise. "Twenty seven more days!” they write in an Instagram post.

The date is so embedded in the first friend's mind that frankly, others around them are a little worried. What will happen if they close in on their due date and there's no sign of labor? What if they sail right on past it? Will they be disappointed and impatient? Will they start doubting their body? They can't cancel the trip, but they might be tempted to change their travel plans.

The other friend, on the other hand, is taking a different approach. They know they're going on a "cruise" pretty soon. They're packed and ready to go, but they're not sure of the actual launch date. If labor doesn't start by their due date, they won't be disappointed, because they didn't have a firm date in their mind. They know to expect labor soon, but they're also realistic that there could be some unexpected delays or surprises along the way.

Now, everyone's experience of pregnancy is different, and there's no "right" or "wrong" way to approach your estimated delivery date, but it could be argued that a more relaxed and flexible approach might help you get to the finish line a little bit easier—and it certainly sets the stage for the unpredictable nature of parenthood.

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Sources
Parents uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Methods for Estimating the Due Date. American College of Obstetricians and Gynecologists. 2017.

  2. Length of human pregnancies can vary naturally by as much as five weeksScienceDaily. 2013.

  3. Births: Final Data for 2021. National Vital Statistics Reports. Centers for Disease Control and Prevention. 2023.

  4. Management of Late-Term and Postterm Pregnancies. American College of Obstetricians and Gynecologists. 2014.

  5. Reliability of Last Menstrual Period Recall, an Early Ultrasound and a Smartphone App in Predicting Date of Delivery and Classification of Preterm and Post-Term Births. BMC Pregnancy Childbirth. 2021.

  6. Use of time to event analysis to estimate the normal duration of human pregnancy. Hum Reprod. 2001.

  7. Predicting Date of Birth and Examining the Best Time to Date a Pregnancy. Int J Gynaecol Obstet. 2013.

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