Calculate your due date, current pregnancy week, trimester, and key milestones. Includes RANZCOG antenatal care schedule and week-by-week baby development guide.
Your estimated due date is usually worked out by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP), a method called Naegele's Rule. If you know your conception or IVF transfer date, the calculator counts forward from there instead. Only about 1 in 20 babies arrive exactly on the due date — it is an estimate, not a fixed appointment.
| Milestone | Date | When |
|---|
| Week | Appointment / Milestone | Your date |
|---|
Source: RANZCOG — Royal Australian and New Zealand College of Obstetricians and Gynaecologists. Schedule may vary with your healthcare provider.
| Week | Baby size | Key development |
|---|
There are three common ways to date a pregnancy, depending on which date you know.
Pregnancy is divided into three trimesters, each about three months long, tracked in weeks from your last period.
| Trimester | Weeks | What's Happening |
|---|---|---|
| First | 1–12 | Major organs form; early symptoms common |
| Second | 13–26 | Baby grows; movements often felt; energy often improves |
| Third | 27–40 | Rapid growth; preparing for birth |
These are general developmental milestones. Every pregnancy is different, and your care team tracks your own progress.
| Around Week | Milestone |
|---|---|
| 6–8 | Heartbeat often detectable on ultrasound |
| 12 | End of first trimester; first-trimester screening |
| 18–22 | Detailed anatomy (morphology) ultrasound |
| 24 | Viability milestone; glucose screening around now |
| 28 | Third trimester begins |
| 37 | Considered full term from 37 weeks |
| 40 | Estimated due date |
Both methods estimate how far along you are, and they usually agree closely. When they differ, ultrasound dating is generally more accurate, especially if your cycle is irregular.
| Feature | LMP Dating | Ultrasound Dating |
|---|---|---|
| Based on | First day of last period | Direct measurement of the baby |
| Assumes regular cycle? | Yes (28-day) | No |
| Most accurate | If cycles are regular | Early pregnancy (8–14 weeks) |
| Used for | Initial estimate | Confirming or adjusting the date |
In Australia, antenatal care is coordinated through GPs, midwives, and obstetricians. Medicare covers most routine antenatal appointments. The Pregnancy, Birth and Baby helpline (1800 882 436) provides free information and support 24/7.
Naegele's Rule: EDD = LMP + 280 days (40 weeks), adjusted for cycle length variations from 28 days. Ultrasound dating in the first trimester is the most accurate method and takes priority over LMP-based calculation.
1st trimester: Weeks 1–12 | 2nd trimester: Weeks 13–27 | 3rd trimester: Weeks 28–40+
Select your calculation method — Last Menstrual Period (LMP) is the standard, but you can also use a known conception date, a known due date (to work backwards), or IVF transfer dates. Enter the relevant date and your average cycle length if using LMP. Click Calculate to see your estimated due date, current week, trimester, and key upcoming milestones.
The LMP method (Naegele's Rule: add 280 days to the first day of your last period) is the standard starting point and the method this calculator uses. However, first-trimester dating ultrasounds — typically performed at 8-14 weeks — are more accurate because they measure the baby directly. If your ultrasound date differs by more than 7 days from your LMP-calculated date, your clinician will typically use the ultrasound date as the official EDD (estimated due date).
Medicare covers most routine antenatal appointments through your GP or public hospital antenatal clinic. Key appointments and screening timelines under the RANZCOG schedule include:
The Pregnancy, Birth and Baby helpline (1800 882 436) provides free information and support 24 hours a day, 7 days a week, including connection to a maternal child health nurse.
Naegele's Rule adds 280 days to the first day of your last menstrual period assuming a 28-day cycle. Known conception date: add 266 days. An early ultrasound at 8–14 weeks refines the estimate by directly measuring the baby.
Only a small percentage of babies arrive on their exact EDD. Most deliveries occur within 1–2 weeks either side. Your clinician may adjust the date after the dating ultrasound.
Pregnancy, Birth and Baby helpline: 1800 882 436 (free, 24/7, connects to a maternal child health nurse). Medicare covers most routine antenatal care through your GP or public hospital antenatal clinic.
Your weeks of pregnancy are counted from the first day of your last menstrual period, not from conception. So at the time of conception you are already considered about two weeks pregnant. Enter your last period date in the calculator to see your current week and trimester.
A due date is an estimate, not a fixed date. Only around 5% of babies arrive exactly on their due date; most are born within two weeks either side. Early ultrasound dating is the most accurate method. Your care team uses the due date as a guide for monitoring your pregnancy.
Yes. With IVF, the dates are known precisely, so due dates are very accurate. The calculation counts forward from your transfer date and adjusts for the age of the embryo (for example, a day-5 blastocyst). Enter your transfer details and the calculator estimates your due date.
The estimated due date for twins is calculated the same way (40 weeks from your last period), but twins are very often born earlier than a single baby. Many twin pregnancies are delivered before 38 weeks, so your care team will monitor you more closely and discuss timing with you.
If your cycle is irregular or longer or shorter than 28 days, the last-period method is less reliable, because it assumes ovulation around day 14. In that case an early dating ultrasound is especially useful, as it measures the baby directly rather than relying on your cycle.
If you know the date of conception (for example, from ovulation tracking or IVF), add 266 days to estimate the due date. This is 14 days fewer than the last-period method, because conception normally happens about two weeks after your period starts.
A home pregnancy test is usually accurate from the first day of a missed period. If it is positive, book with your doctor or midwife to confirm the pregnancy and arrange early antenatal care and dating. Seek prompt medical advice for severe pain, heavy bleeding or other worrying symptoms.