Due date calculator
Work out your estimated due date from the first day of your last period, your conception date, or an IVF embryo transfer. You’ll also see how many weeks pregnant you are and when the usual Australian scans and tests fall.
An estimate, not a diagnosis. An early ultrasound is the most accurate way to date a pregnancy, and your midwife or doctor may change your due date after one. Nothing you enter leaves this device.
How this due date is worked out
- From your last period (Naegele’s rule): due date = first day of your last menstrual period (LMP) + 280 days (40 weeks). This assumes a 28-day cycle with ovulation around day 14.
- Longer or shorter cycles: ovulation shifts later or earlier, so the calculator adds or takes away the difference from 28 days. A 35-day cycle moves the due date 7 days later.
- From conception: due date = conception date + 266 days (38 weeks).
- After IVF: the embryo’s age is known, so the due date = transfer date + 261 days for a day-5 embryo (blastocyst), or + 263 days for a day-3 embryo.
- Ultrasound wins: if an early scan (before 14 weeks) differs from your period dates by more than about a week, the scan date is usually used instead.
Pregnancy is counted from the first day of the last period, about 2 weeks before conception. So at “4 weeks pregnant”, the embryo is about 2 weeks old.
Key dates in pregnancy (Australia)
- Dating ultrasound: 8 to 14 weeks, mainly to confirm the due date, especially if your period dates are unsure.
- NIPT (non-invasive prenatal testing): an optional blood test from 10 weeks that screens for some chromosome conditions. It isn’t covered by Medicare, so there’s usually a private cost.
- Combined first trimester screening: an optional blood test plus a scan of the back of the baby’s neck, at about 11 to 13 weeks.
- Morphology (anatomy) scan: 18 to 20 weeks, to check how the baby and placenta are developing.
- Whooping cough vaccine: ideally 20 to 32 weeks of every pregnancy. The flu vaccine can be given at any stage.
- Glucose tolerance test: 24 to 28 weeks, to check for gestational diabetes. Some people are tested earlier.
- RSV vaccine: from 28 weeks, preferably by the end of 36 weeks, to protect the baby in the first months of life.
- Term: babies born from 37 weeks are term. The due date is 40 weeks.
When to get help
Call your midwife, GP, maternity unit or 000 straight away for:
- Bleeding from the vagina, or fluid leaking
- Strong or ongoing tummy pain
- A bad headache, blurred vision, or sudden swelling of the face or hands
- A fever, or feeling very unwell
- Your baby moving less than usual, or a change in the pattern of movements, later in pregnancy
In Australia, the free Pregnancy, Birth and Baby helpline is 1800 882 436 (7am to midnight AET, every day).
Common questions
How is my due date calculated?
Most calculators, including this one, use Naegele’s rule: the first day of your last period plus 280 days (40 weeks), adjusted if your cycle is longer or shorter than 28 days. If you know your conception or IVF transfer date, the calculator uses that instead.
How accurate is a due date calculator?
It gives a good estimate if your periods are regular and you’re sure of the date. Only a small share of babies arrive on the due date itself; birth any time from 37 weeks is term. An early ultrasound (before 14 weeks) is the most accurate way to date a pregnancy.
How do I work out my due date after IVF?
Use the transfer date and the embryo’s age. For a day-5 embryo (blastocyst), add 261 days. For a day-3 embryo, add 263 days. Your fertility clinic will also give you a due date.
What if my cycle is longer than 28 days?
Ovulation usually happens later in a longer cycle, so your due date moves later too. This calculator adds the extra days: a 35-day cycle makes the due date 7 days later than the standard rule. If your cycles are irregular, an early dating scan is more reliable.
When is the dating scan in Australia?
Usually between 8 and 14 weeks of pregnancy. It confirms how far along you are, checks for twins, and can change your due date if it differs from your period dates.
Sources
- ACOG Committee Opinion 700: Methods for estimating the due date (2017, reaffirmed). 280 days from LMP; IVF: transfer + 263 days (day-3 embryo) or + 261 days (day-5 embryo); when an early scan should change the due date
- Australian Government Department of Health: Pregnancy timeline fact sheet (2025). dating scan 8 to 14 weeks; morphology 18 to 20 weeks; glucose test 24 to 28 weeks
- ADIPS 2025 consensus recommendations on gestational diabetes (Med J Aust). 75 g glucose tolerance test at 24 to 28 weeks; earlier testing for some
- RACGP, Australian Family Physician: Noninvasive prenatal testing. NIPT from 10 weeks; combined first trimester screening at 11 to 13 weeks
- Australian Immunisation Handbook: vaccines recommended in pregnancy. whooping cough ideally 20 to 32 weeks; RSV (Abrysvo) 28 to 36 weeks; flu vaccine at any stage
- Pregnancy, Birth and Baby: checkups, scans and tests