Due date calculator
Your estimated due date is 40 weeks (280 days) from the first day of your last period, or 38 weeks from conception or an IVF transfer. Enter the date you know and Hello Bub gives you the due date, how many weeks you are today, your trimester and the dates of your 12-week scan, morphology scan, glucose test and Parental Leave Pay claim.
How the due date is calculated
Doctors and midwives in Australia date a pregnancy from the first day of the last menstrual period (LMP), even though conception happens about two weeks later. That is why you are "4 weeks pregnant" at the time of a positive test. The calculator adds 280 days to your LMP (Naegele's rule), adjusts for a cycle longer or shorter than 28 days, and for IVF counts 266 days from egg collection: 263 from a day-3 transfer, 261 from a day-5 transfer.
Why your scan date wins
A dating ultrasound between 8 and 13 weeks measures the baby from crown to rump and is accurate to about five days. If the scan date differs from the LMP date by more than a week, Australian hospitals use the scan. Enter the scan's date and gestation and the calculator will do the same; update the due date in your plan if it moves.
How accurate is a due date?
About 1 in 20 babies arrives on the due date itself. Most are born between 38 and 42 weeks; a first baby arrives a little later on average. Term starts at 37+0, and Queensland public hospitals offer induction from 41+0 and by 42+0 if labour has not started.
What happens next
Questions about due dates
Can I calculate my due date from the conception date?
Yes. Choose "Conception date" and the calculator adds 266 days. It is a good option if you tracked ovulation.
How do I calculate my IVF due date?
Choose "IVF transfer", enter the transfer date and whether the embryo was day 3 or day 5. The calculator counts back to the notional egg collection and forward 266 days.
When will I be 12 weeks pregnant?
The result card shows the date your 12-week (11+0 to 13+6) scan window opens and closes; that is also when combined first-trimester screening is done.
Does the due date change with a longer cycle?
Yes. A 35-day cycle moves the due date about a week later than the 28-day assumption. Enter your usual cycle length and the calculator adjusts.
Is this calculator Australian?
Yes. The dates it produces follow the Australian Pregnancy Care Guidelines schedule and the Services Australia claim windows, not US or UK timings.
Written by the Hello Bub team. The medical schedule follows the Australian Pregnancy Care Guidelines and the National Immunisation Program; money sections follow the Services Australia and Fair Work rules current for 2026–27; last reviewed 3 November 2026.