Estimated DOB

Estimated Date of Birth

Pregnant and wondering when your baby might be due? Congratulations!

Only around 3-5% of babies are born on their Estimated Date of Birth (EDB) with full term pregnancy classed between 37-42 weeks of pregnancy.

A date based on your last menstrual period is most accurate, because ultrasound has a margin of error even at early stages, and is based on mathematical averages. Your body offers the most reliable estimate.

If you are given two due dates, it’s a great idea to take the one which is furthest away, because you’ll have less pressure for an induction. It is well known that induction for a non-medical reason increases your chances of interventions such as epidural, instrumental birth and Caesarean Section (C/S). So if you want a normal birth and your baby is healthy, it is best to await spontaneous labour as this indicates your baby is ready to be born.

Expected date of Birth (EDB) is conventionally calculated using Naegele’s Rule as a standard way of calculating the due date for a pregnancy.

The rule estimates the EDB by adding one year, subtracting three months, and adding seven days to the first day of a woman’s last menstrual period (LMP). The result is approximately 280 days (40 weeks) from the LMP. This rule has an inherent flaw of presuming the menstrual cycle of the woman being regular and of 28 days duration.

In case of women whose cycles are more (or less) than 28 days this formula gives an erroneous result. However when you meet with your midwife she will spend time with you asking about and taking in to consideration the duration of your previous menstrual cycles and family birthing history. She will then discuss with you an estimated due date which is unique to you.

See EDB Calculator below and discuss with your midwife at your booking in appointment as there maybe other variables to consider in the calculation.

Please remember that your baby will come when it is ready, so any calculated result is an estimate only.
Franz Karl Naegele OB, 1778–1851
  • Due Date Calculator
    First day of your last menstrual cycle
    Normal length of your menstrual cycle
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Important information to remember regarding your due date:

Few women give birth on their actual due date and the majority of babies are born from 39-41 weeks of pregnancy. This is a fairly large window, beginning 3 weeks before and extending to 2 weeks after the due date. As a result, any pregnancy that occurs during this time frame (between 37 and 42 weeks) is regarded as full term.

A small percentage of women give birth early, before 37 weeks; while the remainder give birth after the 42nd week.

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!), your midwife will discuss all your options with you and together agree on a management plan that suits your individual wishes and needs.