due date calculator

Pregnant and wondering when your baby might be due?

BellyBelly’s due date calculator below will give you an estimated date of birth for you to mark on your calendar.

Due Date Calculator Accuracy

Despite having an estimated date of birth, please bear in mind that only 3-5% of babies are born on their due date — or “guess date” if you prefer! Full term pregnancy is classed between 38-42 weeks of pregnancy. The date a due date calculator will give you is based on 40 weeks of pregnancy, which is right in the middle of full term.

Some women have ultrasounds to check on their estimated due dates. However, one study found that adjusting a baby’s estimated due date as a result of a first trimester dating ultrasound did not reduce the incidence of induction of labour. Another recent study in 2013 found that even where the date of ovulation was known, the length of pregnancy varied by 37 days — even if they excluded women who had complications or preterm births.

So when you try BellyBelly’s due date calculator (with adjustable cycle lengths) you will be able discover an approximate date when your baby will arrive, but keep fluctuations in mind.

In the due date calculator below, you’ll notice that by making slight adjustments to your cycle length and luteal phase in the calculator below, it can effect the due date. This is because most of our bodies don’t run to the averages which standard due date calculators or charts use (which is the same as a doctor or midwife would use). Given that many women don’t know their cycle length and luteal phase, you can begin to see why it’s called an ‘estimated’ due date!

Trust Your Baby… He Knows His Due Date, Not Anyone Else!

Unfortunately, no doctor — nor any due date calculator — will be able to give you an exact due date. The vast majority of babies know when it’s time to be born based on their own physical and developmental readiness. So for this reason we encourage you to remember that a pregnancy is still classed as full term up to 42 weeks. Rest assured if you do go post-dates (as frustrating as it may be!), in a healthy pregnancy, remind yourself that you are giving your baby the best chance to be born happy and healthy. Of course, being patient can mean less intervention and a better recovery for you too. Routine and unnecessary inductions only add to possible complications — including caesareans — and traumatic births.

Give your healthy, unborn baby a most precious gift of allowing him or her to arrive on their own birthday. Check out our article, 40 reasons to give your baby (at least!) 40 weeks, here.


Defaults to an average of 28 days; please adjust if required.

Defaults to an average of 14 days; please adjust if required.


Kelly Winder is a birth attendant (aka doula), the creator of BellyBelly and mum to three beautiful children. Become a fan of BellyBelly on Facebook or add Kelly here. BellyBelly is also on Twitter. Please note that all of my suggestions and advice are of a generalised nature only and are not intended to replace advice from a qualified professional. BellyBelly.com.au – The Thinking Woman’s Website For Conception, Pregnancy, Birth and Baby.