How Your Due Date is Calculated

Among the big questions that future moms and dads usually ask themselves is how the due date is calculated. Although the precise moment can't be known with exact certainty, nowadays there are some methods to make the best educated guess possible.
How Your Due Date is Calculated

Last update: 18 July, 2018

When a woman first finds out she’s pregnant, one of the most common questions is when her baby will be born. There are a few ways we can calculate an approximate due date, with the use of simple mathematical formulas to medical tables consulted by specialists.

Regardless of the methodology, the essential thing is for the woman to know when her last menstruation date was.

Women’s fertility cycles can help identify the moment when conception probably happened. You can calculate this with the first date of your last menstrual cycle.

After 14 days, the ovum is the most fertile. It’s at that moment when it’s assumed that it could be fertilized. This period of maximum fertility for a woman lasts two to three days.

What Formulas Calculate the Possible Due Date?

The two common metrics on how you can calculate the possible date of delivery are the Naegele’s Rule and the medical calendar. 

The first consists of a mathematical formula from the date of the last menstruation. From there, you subtract three months and add seven days.

If we give an example with real dates, we can think that, if the menstrual cycle was on May 11, the possible date of delivery will be February 18.

In the  case of the medical calendar, it can be shown as a wheel or a table and is very common in doctor’s offices.

If we take the method of the tables, in the left column it indicates the month of the last period and in the top row the days. Between the month and the day, there is a line indicating the possible due date.

You can find other methods to calculate the due date on the internet. There are many digital calculators that work very well. In all of them, the common requirement is the date of the last menstruation.

However, only 10% of women give birth on the date indicated by these calculators.  

How Your Due Date is Calculated

Benefits of Knowing the Possible Due Date

A pregnancy is considered full term when the baby is born between weeks 38 and 42. Knowing this, specialists offer the mother a range of time that she could possibly give birth.

The main objective of this information is that the mother has the opportunity to prepare herself both physically and psychologically. In addition, she can prepare everything necessary for the arrival of the baby.

The truth is that the due date can vary between two weeks before or after the indicated day.

Depending on the type of pregnancy and the conditions of the mother, some specialists reserve the possible date of delivery. Although they usually tell the mother the month of birth, they don’t specify the date. This decision type may be used with mothers who are very anxious or have blood pressure disorders associated with emotional changes.

“Fertility cycles of women allow us to identify the moment when conception probably happened.”

How to Know if the Baby is Ready to be Born

Many specialists await the results of the ultrasound during the 12th week. In this test, they pay attention to the baby’s measurements and evolution.

Taking into account these values ​​and the mother’s age, they can estimate a more accurate due date.

How Your Due Date is Calculated

The ultrasound at week 12 even allows specialists to identify abnormalities in the fetus. Between 60 and 70% of genetic malformations or congenital anomalies can be identified in this checkup. For example, Down Syndrome is one of them, as are problems related to the heart and blood vessels.

Another benefit of having an ultrasound at week 12 is that doctors can identify multiple pregnancies. 

They can also find out the pelvic capacity of mothers for when they give birth. On the other hand, the results of this ultrasound can even reveal certain possibilities of medical complications during pregnancy.

The possible due date allows future parents to adapt their home and routines  for their baby’s arrival.

The important thing is to recognize that the due date may be pretty flexible; no matter how many analyses specialists perform, it won’t be possible to know the due date with absolute certainty.

All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

This text is provided for informational purposes only and does not replace consultation with a professional. If in doubt, consult your specialist.