Pregnancy due date calculator

How does the due date calculator work?

Generally, you ovulate 2 weeks after the first day of your period, and will conceive shortly after that.

The average pregnancy lasts between 37 and 42 weeks, so it is possible to give a due date based on all of this information - though there will probably be a bit of wriggle room on either side.

How likely is it my baby will arrive on my due date?

Actually - it's not very likely that they'll arrive dead on the actual predicted due date. Data from the Perinatal Institute suggests only 4% of babies arrive on the exact day predicted.

And anecdotal evidence from our Facebook community backs this up. Debbie H says:

“First born 6 days late, 2^nd born 1 day early, 3^rd born 2 weeks early, 4^th born 1 day late!”

Though - that's not always the case. A few of our mums, like Natasha B, had very punctual babies: “All 3 of mine came on their due date x.”

If you’ve been tracking your pregnancy efforts closely - perhaps using a tool like our ovulation calendar - you might be able to pinpoint a day when you reckon there’s a good chance you conceived (most likely, a day around ovulation, when you had sex).

And, believe it or not, some women do say they just knew the moment they were pregnant (read those stories here) – in which case, if you pass this onto your doctor or midwife, they may well be able to give you a more accurate due date than without having this info.

Is your first baby more likely to be late?

According to some studies, yes, firstborns are more likely to be late. A 2002 study of 9,148 live births in the USA did find a slightly higher incidence of first babies being born at 41 weeks or later - in fact, first babies have a 15-16% chance of being born early as opposed to a 9-10% chance with other babies.

• More on first babies being late

However – don’t bank on this happening, as plenty of mums have experienced having early first babies, too. In our Facebook community, Kate M says: “My first was born 37+3. Massive shock I was so unprepared and thought I had ages. Thank God for 24hr Asda"

And MFM team mum Tara B reveals: “I finished work on Friday, expecting to have 3 weeks off before my first and only baby was born. But my waters broke on the Saturday and I had her on the Sunday. We didn’t even have a bed for her!”

Will my due date change after a scan?

Possibly, yes. On our forum, mum AbnormalKitty says: “I had an early scan at 8 weeks, which put me back a week. Then at my 12-week scan, they put me forward by 4 days.”

Your 12-week scan is also known as your dating scan. As well as checking your baby is growing healthily it will also be used to try and give a due date, known as an EDD (an estimated due date (and the ‘estimated’ is quite important here!)

• Can your pregnancy scan give the wrong due date?

Bearing all this in mind, though, we reckon it’s still pretty handy to have a due date noted – as, even if your baby doesn’t come right on time, it gives you something to work towards as you go through your pregnancy.

Read more

• I’m pregnant – what should I do next?
• Everything you need to know about growth scans in pregnancy
• 13 of the best pregnancy apps