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When Is My Baby Coming? How to Calculate Your Due Date.

Every pregnant woman wants to know when her due date will be. When is it due? However, this can be a difficult question to answer because due dates are calculated based on the mother’s last menstrual period and many women don’t accurately track their periods. Fortunately, our due date calculator makes it easy for you to find out when your baby is due!

Use our Due Date Calculator

You can use our due date calculator to find out when your due date is. As you’ll learn later, this will only give you an approximation of when your baby will arrive.


What is a Due Date?

You can’t predict the day of your baby’s arrival, but you will likely hear this question when pregnant. The medical world refers to it as EDD which is short for the estimated date of delivery. You’re not likely to deliver on that due date – more accurately it should be called an estimate and a better way would be “EDD” or estimated date of delivery.

How to Calculate the Due Date?

When you’re pregnant, there’s so much to think about. What are the four things that determine your due date? You might not know them all! But we do, and they’re figured into our due date calculator right here on this page.

Last Menstrual Period

The most common method for calculating the due date is to find the first day of your last menstrual period. Simply add 40 weeks, or 280 days, to that date—and voila! This will be when you’re due.

Date of Ovulation (Conception Date)

If you’re like most women, you can’t pinpoint the first day of your last menstrual cycle. That’s ok because you can also calculate the due date by figuring out the date of ovulation.

In fact, many women have a better recollection of when they had sex than when their last period started! If you’re using an average 28-day cycle and your cycles are pretty consistent in length, then you’ll know when your baby was conceived. By knowing your ovulation date, you can also calculate an estimated due date by adding 266 days to it.

calculate ivf due date

IVF Transfer Date

We would be remiss to leave out our IVF mommies. If you used in-vitro fertilization to get pregnant, there are two ways to calculate your due date.

  • IVF 3-Day Transfer Date – You can calculate your pregnancy due date by adding 263 days to the last day of your IVF transfer. This will give you an exact figure so that we know when it is safe for your family, friends, and coworkers to start getting ready!
  • IVF 5-Day Transfer Date – You can calculate your due date by adding 261 days to the last day of your IVF, that’s when you’ll have a baby. At least, that’s if you’re going by the book.

Ultrasound Scan

Rather than guessing, you can also get an ultrasound scan, whether with your OB/GYN, or here at our studio.

Ultrasounds measure all sorts of measurements such as crown rump length, abdominal circumference – everything needed in order to determine how far along you are. Once you know how far along you are, you can better plan and forecast out your due date.

Crown rump length (CRL) is the length of the embryo or fetus from the top of its head to bottom of torso. It is the most accurate estimation of gestational age in early pregnancy, because there is little biological variability at that time.

How Accurate are Due Date Estimations?

It’s important to understand how accurate due date estimations are, and that there is a margin of error.

In general, the due date estimation will be within two weeks or so from your actual due date.

According to the Perinatal Institute, a non-profit organization, an EDD is rarely accurate – in fact, a baby is born on its predicted due date just 4% of the time.

Additionally, About 57% of deliveries take place between 39- and 40-weeks gestation (full-term).

Some exceptions to due-date estimation accuracy can include:

  • Twins
  • Triplets or more
  • Breech babies (babies that come out feet or buttocks first)

So, don’t get too wrapped up in due date estimations. Only your baby knows when they’ll enter the world. The rest of us are just taking educated guesses.

Why a Pregnancy Calculator Can Only Give an Estimate

Here are a few reasons why pregnancy calculators can only give you an estimated due date:

Menstrual Cycles Can Differ

Women typically experience a menstrual cycle every 28 days, but there are many factors that can affect the length of their cycles. For example, some women may have irregular ovulation timing and even longer intervals between menstruations in addition to shorter ones due to stress or illness. Furthermore, this calculation method is based on an average woman with regular periods–some ladies have a menstrual cycle as often as once per month!

Baby Birth is Mysterious

The mystery of the birth process is one that goes all throughout human life. A baby’s development can be mysterious, as there are no set guidelines for when they will develop certain abilities like hearing or walking on their own. It could take just a few days or months before babies start to get some skills and it might even happen at different times in each pregnancy too!

Pregnancy Complications

Pregnancy complications mean that the delivery timeline can change. Sometimes, a woman’s labor is induced to prevent harm coming to them or their child and this will drastically alter your baby’s arrival time in some cases so it pays off for you better prepare yourself now.

What are the Stages of Pregnancy?

There are multiple ways to calculate your due date because pregnancy is not always the same length for every woman.

Trimesters Explained

trimesters explained infographic
  • First trimester: This is the first three months of pregnancy and it’s when you will be most likely to feel some symptoms like nausea or fatigue.
  • Second Trimester: The second trimester is called a “golden time” because your baby’s brain, muscles, heart, and circulatory system are all developing while he or she is growing.
  • Third Trimester: The last part of pregnancy is the third trimester. It can be difficult because you are carrying more weight due to your growing baby and may not feel very comfortable

There are other “terms” you should know about, like 40 weeks gestation which means that at this time your baby will be considered full-term and can safely survive outside of mom’s womb with medical care if needed.

According to the American College of Obstetricians and Gynecologists:

  • Early Term is a gestation period between 37 weeks – 38 weeks pregnant and 6/7 days
  • Full Term is a gestation period between 39 weeks – 40 weeks pregnant and 6/7 days
  • Late-Term is a gestation period between 41 weeks – 42 weeks pregnant and 6/7 days
  • Post-term is when the gestation period is longer than 42 weeks pregnant.
calculate due date with pregnancy test

Can a Due Date Change?

Like we mentioned earlier, due dates aren’t set in stone.

Your OB/GYN may change your due date based on what they see. Reasons why your due date may shift:

  • If your baby is noticeably smaller or larger than “the average,” then the doctor will be inclined to revise their estimations accordingly 
  • Irregular periods can throw off a pregnancy’s estimated length.
  • Abnormal fundal height (size of uterus).
  • Abnormal levels of proteins produced by your growing baby (Alpha-fetoprotein).

What to Do After Calculating Your Due Date

Once you’ve calculated the due date, it’s time to start making the “due date” part of your daily routine.

Start using our due date calculator as a guide for what to expect in the weeks before and after birth. You should also:

Visit your Doctor

At this point, you should be getting regular prenatal checkups with your doctor or midwife that will help keep track of your pregnancy.

Find Out your Baby’s Gender

If you haven’t already, and if you want to know, now’s the time to find out whether it will be a boy or girl.

Our SneakPeek Early Gender DNA Test can help mothers to know their baby’s gender as early as 8 weeks in. Knowing the sex of your child is one way that you get an insight into what they will be like as a person, which can create a connection between them and you long before they are born.

Having problems convincing your husband to find out the baby’s gender early? Here are some tips that may help you.

Schedule your SneakPeek Early Gender DNA Test Today.

If you’re eager to find out your baby’s gender, now there is a way that can be done as early as 8 weeks into the pregnancy. Knowing the gender of their baby gives expectant moms an opportunity to plan around how they want their nursery decorated and choose clothes for themselves and their new little one.

You don’t have to wait until after birth to learn whether your baby is a boy or a girl—schedule your SneakPeek Early Gender DNA Test today!


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