How to calculate your due date

The test is positive and as the reality sinks in, you reach for your calendar to mark down the big day. Do you count nine months from today or when you think you conceived? Is it 40 weeks or nine months? The confusion begins. Don’t worry — it’s not as hard as it seems. We’ll show you how to easily calculate your due date.

Calculate your due date – it’s all numbers, numbers, numbers!

As a matter of convenience, a pregnancy is usually calculated to 40 weeks long, but only about five percent of babies actually stay in the womb 40 weeks to the day. A full-term pregnancy is considered to be between 38 weeks and 42 weeks long. A baby born at 38 weeks isn’t early and a baby born at 42 weeks isn’t late. You should look at 38-42 weeks as a range, and 40 weeks as an average. Anything around this range is fair game for you to have your baby.

Calculate your due date – the art of conception

And the confusion continues. The 40 weeks we isn’t counted by the date you conceived. It’s actually counted from the first day of your last menstrual cycle. You might think this is strange but it actually makes sense. You know the date you started your period, but do you know the exact day you ovulated? If you do, you’re very unlikely to know the exact day you actually conceived.

An egg can be fertilized up to 24 hours after ovulation occurs, sometimes longer. A sperm can stay active in the vaginal secretions for three days after intercourse. Even if you know the day and time your egg was released, you don’t know the date sperm and egg got together. This explains why the first day of your pregnancy starts on the first day of your last menstrual period.

The last menstrual period method is not 100% but is the most closely correct way to calculate your baby’s date of arrival. Like everything else, only your doctor can tell you’re the best date for your baby to arrive.

How to calculate your due date

Find out how to work out your due date on the next page…