Many pregnant women are impatiently awaiting the birth of their child. Comparing pregnancy weeks, ultrasound images and birth plans is a popular pastime among mums-to-be. But in order to really maximise the excitement, they first need to know their baby’s estimated due date.
How to calculate due date and pregnancy week? Why is it important to know the expected date of delivery? How accurate are due date calculators? And does cycle length matter?
Please note:
The information provided by the due date calculator is for general information purposes only and is not intended as a substitute for professional medical advice or treatment. Please consult your GP or your midwife for an accurate diagnosis.
Due date calculator: Why is it important to calculate the due date?
Pregnancy due date calculator: different calculation methods
How accurate are due date calculators?
Due date calculator: why does cycle length matter?
A final word on pregnancy due date calculators
Knowing their baby's due date has several advantages for parents-to-be. First of all, knowing the estimated date of delivery makes it much easier to get properly excited. However, knowing what pregnancy week you’re in also has other advantages, such as:
During your first appointment with your GP or midwife, you will get official confirmation of your pregnancy. As part of the appointment, your GP or midwife will also calculate your baby’s estimated due date. However, the calculation method for determining the due date can be a bit confusing.
So, what is the formula for calculating the due date? Well, there are actually two different methods, which are Naegele’s rule and due date calculation based on the date of conception.
Here is a quick explanation of the two calculation methods:
In addition to the expected due date, your GP or midwife will also determine which pregnancy week you are in. Knowing how far along you are in your pregnancy is important to monitor your baby’s healthy development and better understand the changes that take place in your body. The current pregnancy week is also an important reference for monitoring weight gain during pregnancy.
But how to calculate pregnancy weeks? Well, the first thing you should know is that the first week of pregnancy is not the week following the day of conception. From a medical point of view, pregnancy officially starts 14 days before the conception date, i. e. with the first day of your last period. This means that if you conceived five weeks ago, your GP or midwife will tell you that you are seven weeks pregnant.
That’s why, from a medical point of view, the first day of your last period is more relevant than the actual conception date. The standard reference period for the duration of a pregnancy, which is 280 days or 40 weeks, also starts from the first day of your last menstrual period.
In today’s digital era, a visit to the GP or an appointment with a midwife is not the only way for a pregnant woman to find out how far along she is and when her baby is due. When surfing the internet, it’s easy to find an online due date calculator or an app that can be used for calculating the estimated due date.
Pregnancy due date calculators can use two different types of data for calculating your baby’s due date. They can either calculate the due date based on the date of conception or based on the first day of the last menstrual period.
There is one question that always raises concern among mums-to-be when it comes to due date calculators, and that is how accurate they actually are. The calculation of the due date does, of course, follow clear rules and is therefore mathematically correct. Nevertheless, the calculated due date should only be seen as an estimate since there are many different factors that can influence when your baby finally arrives.
Statistics show that only around 4% of women actually give birth on the calculated due date. The large majority of babies are born within a period of 14 days before or after the calculated due date.
The length of the menstrual cycle varies, meaning that not every woman's cycle is exactly 28 days. In fact, the cycle length can be up to 38 days. Shorter cycle lengths of just 24 days are also possible. For the majority of women, the cycle length is somewhere between 25 and 35 days.
When calculating the due date using Naegele’s rule, the length of the cycle actually has a direct impact on the calculation. That’s because Naegele’s formula bases the calculation on the first day of the last menstrual period. Depending on how many days the mother’s cycle deviates from the regular cycle length of 28 days, a few days must be added or subtracted.
Due date calculators that don’t take the mother’s cycle length into account when calculating the estimated date of delivery, won’t deliver the correct estimate. In cases where the mother’s cycle length fluctuates, the due date calculation is also less accurate than usual.
However, keep in mind that the estimated due date is just that, an estimate of when your baby is likely to be born. In most cases, the actual date of delivery will be a different one.
Online due date calculators are now available on many different websites. Mums-to-be can use them to calculate their estimated due date quickly and easily. Here is an overview of the most important aspects you should keep in mind.