How Accurate Is The Pregnancy Due Date?

How accurate is the pregnancy due date really? When your doctor finally calculates your due date, he or she will make use of every bit of relevant information you can give to estimate (not guarantee) the date you are most likely to put to bed. But you don’t even have to wait for your doctor to estimate your due date, take advantage of our due date calculator and find out in a jiffy.

How Accurate Is the Pregnancy Due Date – How Due Dates Are Calculated

Pregnancy due dates are normally calculated through the Naegele Rule which states that a healthy pregnancy lasts 280 days, or 40 weeks. The first day of pregnancy is taken as the first day of the woman’s last period (LMP). The following equation is used to calculate the due date by our {link.duedatecalculator.0}:

First date of the last period – 3 months +one year +7 days = due date


If first day of your last period is 08/10/2013, subtract 3 months to get 05/10/2013.

Add one year to 05/10/2013 to get 05/10/2014

Add 7 days to 05/10/2014 to get 05/17/2014, which is your due date.

How Accurate Is the Pregnancy Due Date – Why It Is Not 100% Accurate

There are a number of reasons why the pregnancy due date (EDD or EDC) is not always accurate, with the most obvious one being that ovulation time varies from woman to woman. Working with the idea of a healthy pregnancy lasting approximately 288 days, starting with the first date of the last period, then the results are due to differ slightly for every woman.

Other factors that contribute to the inaccuracy of the due date include wrong calculations (when the woman is wrong about or cannot remember her LMP and/or her average cycle), irregular periods, unknown conception date, longer or shorter cycles, and genes. In spite of the fact that your due date is highly likely to be inaccurate, it will still give you a suggestion of when your baby will make an appearance.

How Accurate Is the Pregnancy Due Date – What Statistics Say

Having a full term baby does not necessarily mean having a 40 week old baby, a full term baby can be between 37-42 weeks old, and it is therefore logical to have your baby 2-3 weeks earlier or later than your due date. Statistics show that of all women, only 3-5% deliver on their due date. The majority of pregnant women actually deliver 2-3 weeks after their given due date (70%). The other 25% will either deliver one week earlier or one week later than their due date.

According to recent studies, having an ultrasound done within the first trimester of pregnancy can predict your due date more accurately when compared to other methods used to predict due date. There are, however, no serious complications involved in an inaccurate due date as long as you continue to have regular checkups, especially during the last trimester of your pregnancy.

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