How Many Weeks Pregnant? Everything You Need to Know About Your Due Date

From what they are to how doctors calculate them, read on to learn more about pregnancy due dates—and how you can estimate yours at home.

illustration of pregnant person standing in front of calendar with due date on it
Photo: Getty

You've taken a blood test or an at-home pregnancy test. Two little lines have appeared, and you know you are expecting. You have a "bun" in your proverbial oven. But when will your little one arrive? Well, no one knows—at least not for sure. Pregnancy due dates are estimates, ones which are rarely accurate. Only 5 in 100 people give birth on their due date. Still, they are an important part of pregnancy, as due dates will help you and your doctor best prepare for your little ones arrival.

Here's everything you need to know about due dates, from what they are and how they are calculated to how you can best estimate your baby's arrival at home.

What Is a Pregnancy Due Date, and How Do Doctors Calculate Them?

Your pregnancy due date is an estimation of when your unborn baby will arrive, based on when they were conceived. If you know the exact date—which will most likely be the case when you've used in vitro fertizilation or interuterine insemination—it will make the estimate more accurate. However, even knowing an approximate date is helpful.

What is a due date?

Your estimated due date (EDD) isn't an exact science, but it gives you and your doctor an idea of when your little one will arrive. Estimating a due date makes sure that your unborn baby's development is progressing as it should, to ensure that they are healthy and ready when they finally do arrive.

How is it calculated?

The most common way healthcare providers calculate your pregnancy due date is by counting 40 weeks from the first day of your last menstrual period (LMP). Not all pregnancies last the full 40 weeks, though, and some even might go over that timeline. Not to worry, this is why your due date is an estimate, as opposed to a hard and fast deadline.

What if you can't remember your last period, or they are irregular? In that case, your provider will conduct an ultrasound to get a better idea of when you conceived and when your unborn baby is due.

Are Due Dates Accurate?

Babies don't have calendars—nor do they stick to schedules. In fact, most pregnant people deliver between 37 and 42 weeks. So while your due date can give you an idea of when to expect your unborn baby's arrival, it's not guaranteed.

Pregnancy calculators and due date predictors

There are a plethora of online options for pregnancy calculators and due date predictors. Most calculators follow the same calculation as your doctor's office, but instead of crunching the numbers manually, they do the math for you.

If you're interested in seeing how accurate a calculator is compared to your doctor's estimation, try using the American Pregnancy Association's pregnancy calculator. Keep in mind, however, that you'll need to know your last period date or conception date and how long your menstrual cycle runs.

Are There Any Good Ways to Predict When Baby Will Come?

Even though you have an estimate of when your unborn baby will arrive, there are a few other signs that labor is approaching. In addition to your water breaking and cervix dilating, pay attention to these changes your body may go through.

The baby has dropped

Once your unborn baby is in a head-down position, they'll move into your pelvis to get ready to start heading out the birth canal. Not only might your bump look physically lower, but you'll also likely experience more pressure on your bladder.

You are experieing contractions

You may have experienced Braxton-Hicks, or false labor contractions, throughout your pregnancy. Usually, they go away—if you lay down or drink water—but if your contractions become more regular and/or consistent, it is usually a sign labor is approaching.

You lose your mucus plug and/or have a "bloody show"

No, it isn't the most glamorous-sounding experience in the world, but it is a sign that your unborn baby is making their way out. The mucus plug blocks the opening of the cervix during pregnancy to protect the fetus from bacteria. So once your cervix begins to change and dilate, it will come loose to prepare the way for your little one.

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