Mother and Baby

The Simple Way to Work Out Your Due Date

You may know you’re pregnant, but can you figure out when you're due? 

You’ve now had that pregnancy test confirmation – it’s positive, you’re pregnant. But you want to know exactly when you’re going to be a mum. Is it nine months? 40 weeks from the date of your last period? Or (gulp) six months’ time. Figure out when your baby should arrive using our pregnancy due date calculator.

What is a ‘full-term’ pregnancy?

It’s not as simple as assuming your full-term pregnancy is the day you hit 40 weeks pregnant. In fact, your full-term pregnancy is considered to be anywhere from 38 to 42 weeks. Yes, it’s a due month.

‘On average a pregnancy takes 40 weeks (or 10 lunar calendar months) from the first day of your menstrual cycle or 38 weeks from conception, but there isn’t an exact science to working out your due date,’ says Teresa Walsh, midwife at The Portland Hospital, London.

Count down to baby

To work out your due date, you need to count 40 weeks of pregnancy from the first day of your last menstrual period, even though your baby is technically about two weeks younger than that.

Most women ovulate and conceive two weeks after their last period (or LMP for Last Menstrual Period in fertility speak) and will only be around 38 gestational weeks by the time the pregnancy has reached the 40-week mark.

‘Your dating scan, which you’ll have at 10 to 14 weeks is the most accurate scan to determine your due date,’ explains Teresa.

>Use our Pregnancy Due Date Calculator

Work out your due date a different way

Ready to brush off your GCSE maths? Take the first date of your last normal period, add seven days to that number. Take that date, add nine months, and you get your due month. Simple! Although, don’t be surprised if you add back and find you didn’t have sex on that exact date...

All babies grow at an individual rate and your due date is only an estimation, so be as prepared as you can be for a slightly-earlier-than-expected surprise, or carrying  your baby for a little longer than that date you now have fixed in your head.

Keep in mind that women with irregular cycles may have difficulty calculating their due dates (the LMP method is far from a perfect science), so if you fall in that camp talk to your doctor to get the best estimate of your due date.

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