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How to Calculate the Due Date: When Will Your Baby Arrive?

How to Calculate the Due Date: When Will Your Baby Arrive?

How many more months before you can see, hold, and play with your little bundle of joy? Your OB-Gynecologist might have already informed you of the expected date, but it’s still exciting to compute it on your own. Here’s everything you need to know about the estimated date of delivery and how to calculate the due date.

What is the Due Date?

The due date or estimated date of delivery is the expected date when you’ll give birth to your baby.

Most pregnancies last an average of 280 days or 40 weeks from the first day of your last menstrual period (LMP). But even though we generally consider day one of your LMP as the first day of pregnancy, please note that you probably didn’t conceive until about two weeks after.

While you can calculate your baby’s due date based on the last menstrual period, note that it is not perfect. Still, it is the principle behind the widely-used due date calculator and pregnancy wheels.

Of course, your OB-Gynecologist could also help you determine your baby’s estimated date of delivery through an ultrasound test or your ovulation date. If you’ve had in vitro fertilization (IVF), they would use the date the embryo was transferred.

How to Calculate the Due Date

To calculate the estimated due date, you can use the Naegele’s Rule which makes use of the LMP. Below are the instructions:

  1. Determine the first day of your last menstrual period.
  2. Count back to 3 calendar months from that date.
  3. Add 1 year and 7 days to the resulting date.

Here’s an example of how to calculate the due date.

  1. Let’s say the first day of LMP is June 16, 2021.
  2. Counting back 3 to calendar months would give you March 16, 2021.
  3. Add 1 year and 7 days, and you’ll have: March 23, 2022, as your estimated date of delivery.

You can also use this accurate due date calculator:

Reminder:

Using a calculator helps in how to calculate the due date. It is accurate in terms of computation. However, the result doesn’t often reflect the actual date when you’ll give birth. You’ll only have the estimated date.

Also, do not be surprised if the doctor changes the estimated date of your baby’s arrival. Depending on how your baby’s doing (movement, heartbeat fundal height, etc.), the doctor may move your due date forward or back.

Furthermore, please keep in mind that Naegele’s Rule is based on a 28-day cycle. If you have a shorter or longer cycle, your doctor would make some adjustments.

Finally, if you do not know the first day of your LMP, don’t worry. In most cases, you only need to provide the week of your last period and the doctor would take care of the estimation.

Why is it Important to Calculate the Due Date?

Before your baby arrives, you can start preparing for the maternity go bag and newborn essentials. Additionally, determining when your baby is due helps you file for paternity or maternity leave.

In other words, learning how to calculate the due date helps you plan for your labor and delivery and mentally prepare for parenthood as a whole.

due date calculator

What if You Miss Your Due Date?

Like mentioned earlier, a due date calculator only gives an estimation; so missing your due date by a few days in both directions is usually not a cause for concern. Generally, the doctor would only be worried about premature birth or overdue babies.

Prematurity occurs when the baby is born before the start of their 37th week in the womb. Since preterm birth is a risk factor for various health problems, the doctor would monitor you and your baby closely. It would also help if you watch out for the signs of labor so you could seek medical help as soon as possible.

Late-term pregnancy, when the baby’s still in the womb at 41 weeks to 41 weeks and 6 days, as well as post-term pregnancy, when you still haven’t given birth by 42nd week and beyond, also place you and your baby at risk. If your baby is overdue, your healthcare provider may consider inducing the labor.

Key Takeaways

Your due date is the estimated date of your baby’s arrival. You can learn how to calculate the due date using an app of due date calculator. But please remember that the result is just an estimation.

Missing your due date by a few days is generally nothing to worry about. But if your little one comes prematurely or is overdue, the doctor would want to attend to you and your baby more closely.

Learn more about Being Pregnant here.

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Due Date Calculator

Use this calculator to find your due date. This is just an estimate – not a guarantee! Most women, but not all, will deliver their babies within a week before or after this date range.

Cycle Length

28 days

Hello Health Group does not provide medical advice, diagnosis or treatment.

Sources

Calculating a Due Date
https://www.stanfordchildrens.org/en/topic/default?id=calculating-a-due-date-85-P01209
Accessed June 16, 2021

Pregnancy: Ways to Find Your Due Date
https://www.healthlinkbc.ca/health-topics/aa87660
Accessed June 16, 2021

Using the due date calculator
https://www.nhs.uk/pregnancy/finding-out/due-date-calculator/
Accessed June 16, 2021

How do you calculate your due date?
https://my.clevelandclinic.org/health/articles/10043-calculating-your-estimated-due-date
Accessed June 16, 2021

Baby due date
https://www.betterhealth.vic.gov.au/health/healthyliving/baby-due-date#premature-babies
Accessed June 16, 2021

Overdue pregnancy: What to do when baby’s overdue
https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/overdue-pregnancy/art-20048287
Accessed June 16, 2021

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Written by Lorraine Bunag, R.N. Updated Jun 18
Fact Checked by Hello Doctor Medical Panel