Calculate your estimated due date (EDD) using LMP, conception date, ultrasound, or IVF transfer date. Includes full trimester breakdown and RANZCOG antenatal schedule.
Your due date (estimated date of delivery, or EDD) is most often calculated by adding 280 days to the first day of your last period. If you conceived through IVF or IUI, the dates are known precisely, so the calculation counts forward from your transfer or insemination date instead. This calculator supports all of these methods and gives an estimate to guide your care.
This is an estimate, not a guarantee. Your midwife or doctor confirms your due date, often using an early ultrasound.
| Trimester / Milestone | Date range |
|---|
There are several ways to estimate a due date depending on what you know. IVF and IUI dates are the most precise because the timing is known exactly.
| Method | How It Works | Accuracy |
|---|---|---|
| Last period (LMP) | LMP + 280 days (Naegele's Rule) | Good if cycles are regular |
| Conception date | Conception + 266 days | Good if ovulation date is known |
| IVF (fresh transfer) | Counts from egg retrieval + embryo age | Very accurate |
| IVF (frozen / FET) | Transfer date + (280 − embryo age in days) | Very accurate |
| IUI | IUI date + 266 days | Accurate (timed insemination) |
| Ultrasound | Direct measurement of the baby | Most accurate in early pregnancy |
Because assisted-conception dates are known precisely, IVF and IUI due dates are among the most accurate.
A due date marks 40 weeks, but babies rarely arrive exactly then. Knowing the real spread helps set expectations.
| Timing | Definition |
|---|---|
| Born on the due date | Only about 1 in 20 babies (roughly 5%) |
| Full term | 37 to 42 weeks — most babies arrive here |
| Early term | 37 to 38 weeks and 6 days |
| Post term | 42 weeks or beyond |
First-time mothers, on average, tend to deliver a little later than the due date, though there is wide natural variation.
A "reverse" due date calculation works backwards from a known due date to estimate when conception likely happened — useful for curiosity or record-keeping. Subtract 266 days from the due date for the approximate conception date, or 280 days to find the matching last-period date. Because ovulation timing varies, this gives an estimated window rather than an exact day.
Only a small minority of babies are born on their exact due date. Most births occur between 37–42 weeks (term pregnancy). A first-trimester ultrasound (crown-rump length measurement) is the most accurate method for dating a pregnancy, and takes precedence over LMP-based calculations.
EDD = LMP + 9 months + 7 days (for 28-day cycles). For cycles longer or shorter than 28 days, add or subtract the difference.
For IVF: Day-3 transfer EDD = transfer date + 263 days. Day-5 (blastocyst) EDD = transfer date + 261 days.
The estimated due date (EDD) is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This method assumes a 28-day cycle with ovulation on day 14. For women with irregular or longer/shorter cycles, ultrasound dating in the first trimester (8-14 weeks) provides a more accurate EDD.
| Period | Weeks | Key Developments |
|---|---|---|
| First trimester | Weeks 1–12 | Organ formation, heartbeat detected (~6 weeks), nuchal translucency scan (11-13 weeks) |
| Second trimester | Weeks 13–27 | Anatomy scan (18-20 weeks), fetal movements felt (~18-20 weeks), gender identifiable |
| Third trimester | Weeks 28–40 | Rapid weight gain, lung maturation, Group B strep screening (~35-37 weeks), birth preparation |
| Full term | Weeks 39–40 | Definitions of "full term" vary between organisations; your care provider will advise |
| Preterm | Before 37 weeks | NICU support may be required depending on gestation |
| Method | How the date is worked out | Example (checked against the calculator) |
|---|---|---|
| Last menstrual period (LMP) | LMP + 280 days, plus or minus the difference between your cycle length and 28 days | LMP 1 Jan 2026, 28-day cycle: 8 Oct 2026. Same LMP with a 35-day cycle: 15 Oct 2026 |
| Conception date | Conception + 266 days (equivalent to an LMP 14 days earlier) | Conception 15 Mar 2026: 6 Dec 2026 |
| Ultrasound | Scan date + (280 days minus the gestational age at the scan) | 12 weeks 3 days on 1 May 2026: 10 Nov 2026 |
| IVF, day-3 embryo | Transfer date + 263 days (266 minus 3) | Transfer 10 Apr 2026: 29 Dec 2026 |
| IVF, day-5 blastocyst | Transfer date + 261 days (266 minus 5) | Transfer 10 Apr 2026: 27 Dec 2026 |
Leap years are handled by counting real calendar days. For example, an LMP on 29 February 2024 gives a due date of 5 December 2024. This calculator does not decide which dating method your care team uses. If an early ultrasound and your last period disagree, your midwife or doctor will tell you which date to use.
The LMP method assumes you remember the first day of your last period and that ovulation happened mid-cycle. If your cycles are irregular, you conceived while breastfeeding or after stopping hormonal contraception, or you are unsure of dates, use the result only as a starting point and ask for an early dating ultrasound. Twin pregnancies, a previous preterm birth, or any medical condition mean your care team will plan your timing individually, see the twin pregnancy due date calculator and the IVF due date calculator for those cases. Related tools: ovulation calculator and pregnancy weight gain calculator.
How is a due date calculated in Australia?
Australian midwives and obstetricians use Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period. This is adjusted if your first trimester ultrasound dating differs from LMP dating by more than 5-7 days — ultrasound crown-rump length (CRL) measurement is considered more accurate for women with irregular cycles.
How accurate are due date calculators?
Due date calculators provide an estimated due date, not a guaranteed delivery date. Only a small minority of babies arrive on the exact EDD; most arrive in the weeks around it. When dates are uncertain, an early ultrasound is generally considered more reliable than a calculator based on your last period, and your care provider decides the final due date.
When does each pregnancy trimester start?
First trimester: weeks 1-12 (conception to end of week 12). Second trimester: weeks 13-27. Third trimester: weeks 28 until birth. Full term is defined as 39-40 weeks. Early term is 37-38 weeks; late term is 41 weeks; post-term is 42+ weeks. Preterm birth is before 37 completed weeks.
What is a normal birth weight in Australia?
According to AIHW, the average Australian birthweight is approximately 3.3 kg (3,300g). Low birthweight is defined as under 2,500g. Very low birthweight is under 1,500g. High birthweight (macrosomia) is over 4,000-4,500g. Your care team monitors growth during pregnancy.
How do I calculate my due date with IVF?
With IVF, add days to your transfer date based on the embryo’s age. For a day-5 blastocyst, add 261 days; for a day-3 embryo, add 263 days. Because the transfer date and embryo age are known, IVF dating relies less on remembering your cycle. Your fertility clinic will confirm your dating.
How do I calculate a due date after IUI?
For intrauterine insemination (IUI), add 266 days to your IUI date, since insemination is timed close to ovulation. This is the same method as a known conception date. The date of insemination is known, so this is a useful starting estimate; your clinic confirms dating.
What is a frozen embryo transfer (FET) due date?
For a frozen embryo transfer, the due date is based on your transfer date plus 280 days minus the embryo’s age at transfer. A day-5 frozen blastocyst gives a due date about 261 days after transfer. The transfer date and embryo age are known, so dating does not depend on remembering a last period; your clinic confirms it.
How accurate is my due date?
A due date is an estimate of when you reach 40 weeks. Only a small minority of babies are born on it, but most arrive within the full-term window of 37 to 42 weeks. Early ultrasound dating is the most accurate way to set or confirm your due date.
Can I calculate conception from my due date?
Yes. Subtract 266 days from your due date for the approximate conception date, or 280 days to find the corresponding last-period date. Because ovulation timing varies between cycles, this gives an estimated window rather than one exact day.
Why is my due date different from my dates?
Your due date may be adjusted after an early ultrasound if the baby measures larger or smaller than expected from your last period, particularly if your cycle is irregular. Ultrasound dating is generally more accurate, so providers often use it to set the final due date.
What happens if I go past my due date?
Going past the estimated due date happens. If it does, your care provider will advise on monitoring and the timing of any options. Follow their advice rather than a calculator.