Calculate your baby's due date

Calculate Due Date 1

Determining the date you will give birth is one of the first things you will want to find out once you know you are pregnant. Not only does it have many practical implications – when you will feel tired, when you may have morning sickness, or when you can’t work anymore – but it also puts a bookend on the whole pregnancy and the time from which you will become a mother.

There are several ways to determine when your baby will be due. On average, human pregnancies last 266 days (from conception) or roughly 40 weeks (38 weeks from conception). Of course, nature often takes things into its own hands, so your baby may be earlier or later than the expected due date, which is, in fact, an average of all women. We are all different, our bodies have different physiologies, and we have different family histories, so don’t expect to be able to determine your estimated time of birth down to the last hour.

01 Date of last menstrual cycle

If you know when you had your last menstrual period, you can calculate your approximate due date by adding 280 days to that date.

This works because, on average, it takes 14 days from your last period to actual conception (14 + 266 = 280). However, this relies on you knowing your menstrual cycle and that cycle being regular (e.g. every 28 days).

02 Date of conception

If you know when you actually had sex and were ovulating, you can add 266 days to that date to determine a due date. Of course, this only works if you know your own body’s ovulation cycle, the exact date you had sex, and there weren’t multiple days you had sex during your ovulation cycle.

03 Ultrasound fetal measurements

A doctor can use ultrasound to take measurements while the baby is inside your uterus. These measurements can relate to the length of the baby, the size of its head or its other dimensions. Each of these measurements indicate the approximate age of the fetus (based on average growth rates of fetuses measured over time) and, taken together, can provide a single due date.

This method is likely to be more accurate than the methods above. Performing the ultrasound may also indicate other factors such as the sex of the baby (from 16 weeks) or whether you have twins. Ultrasounds taken over a period of months allows you to see the development of the fetus.

During most pregnancies, you will have an ultrasound at 8-9 weeks, 11-13 weeks and 18-20 weeks. At O&GCG, our obstetricians perform ultrasounds in our rooms at Chelsea House Medical Clinic.

04 I’ve just found out that I’m pregnant – what’s next?

First of all – congratulations! We’re sure you’ve already calculated an approximate due date, so what’s next?

Once you have that positive test, it’s time to call your doctor to schedule your first antenatal appointment. During this appointment, your doctor will confirm your pregnancy and discuss your antenatal care options. This will include whether you will opt for public or private healthcare. If you choose to have your baby as a private patient, your doctor will refer you to your obstetrician of choice. If you’re on the hunt for your perfect obstetrician, you can learn more about our doctors here.

05 Why choose O&GCG for your pregnancy

  • Five female specialist obstetricians: As Dr Jean Wong, Dr Leah Xu, Dr Natalia Khomko, Dr Perri Dyson and Dr Robin Thurman each specialise in different areas of obstetrics, we offer personalised services to every expectant mother.
  • Ongoing care throughout pregnancy and beyond: At O&GCG, your obstetrician is with you throughout your entire pregnancy journey, through delivery and up to six weeks afterwards. Unlike the public system, you will get to know your O&GCG obstetrician on a personal level, and they’ll be present for the birth.
  • Superior support services: In addition to our obstetricians, O&GCG offer a fantastic support team, including Gabi Eckereder (Lactation Consultant) and Robyn Compton (Maternal & Paediatric Dietician).

06 See a O&GCG Obstetrician

At O&GCG, our obstetricians are here for you through every step of your pregnancy and beyond. If you have any questions or concerns, do not hesitate to get in touch.

5 female specialist obstetricians, O&GCG Melbourne, Dr Jean Wong, Dr Leah Xu, Dr Natalia Khomko, Dr Perri Dyson and Dr Robin Thurman

Do you have any concerns or would like to ask our doctors a question?
Please fill in the form below.

  • This field is for validation purposes and should be left unchanged.