Calculating your pregnancy due date

Your baby will spend around 38 weeks inside your uterus. Though the average length of pregnancy is always calculated at 40 weeks. Confused? The reason is because your pregnancy is counted as having begun from the first day of your last period and not the actual conception date (usually around two weeks later).

To help you calculate your due date, simply add seven days to the date of the first day of your last period and then add nine months. So, if your period started on April 1, add seven days (April 8) and then add nine months, which will take you to a due date of January 8.

You may find it easier to use our pregnancy due date calculator.

If your menstrual cycle has been too irregular and you aren’t sure of the date of your last period, an ultrasound will give you a more exact idea of your developing baby’s size and be able to calculate your due date.


Only about 4 percent of women actually have their baby on the due date.

Because some women are not sure about the precise date of their last period, as long as the birth of your baby falls between 37-42 weeks of your due date, your pregnancy will be considered full-term.

If your baby is born prior to week 37 stage of your pregnancy, it will be considered premature. And if your baby is still refusing to budge by week 42 it is officially overdue and your doctor or midwife will discuss the possibility of inducing.


This article was written by Claire Halliday for Kidspot NZ.

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