Due Date Calculator – When Is My Baby Due?


Due Date Calculator - When Is My Baby Due?

Due Date Calculator

Pregnant and wondering when your baby might be due? BellyBelly’s due date calculator will give you an estimated date of birth to mark on your calendar.

Firstly, it’s important to understand that calculating your due date isn’t an exact science.

Please bear in mind only 3-5% of babies are born on the estimated due date (which I call a “guess date”!)

Why is it so low?

A pregnancy is classed as full term between 37-42 weeks of pregnancy.

A due date calculator will give you a result which is 280 days (40 weeks) since your last menstrual period.

It also assumes you have an average cycle length.

That means 28 days in your menstrual cycle, with ovulation on day 14 (which is considered as the conception date).

Bear in mind, 40 weeks of pregnancy is right in the middle of what is considered full term.

This is why so few babies are actually born on this exact day – our menstrual cycles are unique and we conceive at different times in our cycle.

Some women have ultrasounds to confirm how many weeks pregnant they are.

However, the research shows it doesn’t make much difference.

The Research About Due Date Calculations

What does the research say?

One study found that adjusting a pregnancy due date as a result of a first trimester dating ultrasound did not reduce the incidence of induction of labour.

Another 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, this was still the case.

We also know that first pregnancies are typically longer than subsequent.

BellyBelly’s due date calculator has adjustable cycle lengths to help account for differences in cycle lengths.

You’ll notice that by making slight adjustments to your cycle length and luteal phase, it can impact the due date.

So you’ll be able discover an approximate date when your baby will arrive, but keep fluctuations in mind.

Our bodies aren’t based on 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’ date!

Trust Your Baby… He Knows When It’s Time To Be Born!

Unfortunately, no doctor — nor any due date calculator — will be able to give you a guaranteed magic date.

The vast majority of babies know when it’s time to be born, based on their own physical and developmental readiness.

Remember, your pregnancy is still considered full term until you reach 42 weeks.

Rest assured if you do go post-dates (as frustrating as it may be!), remind yourself that you are giving your baby the best chance to be born happy and healthy.

Of course, being patient may mean less interventions, and a better recovery for you and your baby.

Give your healthy, unborn baby a most precious gift of allowing him to arrive on his own birthday.

Check out our article, 40 reasons to give your baby (at least!) 40 weeks, here.

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Enter Your Details In Our Due Date Calculator Below!

First, use our pregnancy calculator below to determine your due date.

All you need to do is enter the first day of your last menstrual period (LMP), then make any cycle adjustments (optional).

Once you’re done, be sure to sign up for BellyBelly’s pregnancy week by week emails – they’re awesome!

You’ll know what to expect and what’s normal every week of your pregnancy.

All the best for an amazing pregnancy.


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.

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