Pregnancy Due Date Calculator
Calculate your estimated due date, current gestational age, trimester, and pregnancy milestones. Use your last period, conception date, or ultrasound results.
Choose Calculation Method
Enter the first day of your last period (Naegele's rule: LMP + 280 days)
How Pregnancy Due Date Calculation Works
Our pregnancy due date calculator estimates your estimated due date (EDD) — also called the estimated date of confinement (EDC) — using three methods: last menstrual period, conception date, or ultrasound measurements.
Method 1: Last Menstrual Period (LMP) — Naegele's Rule
The most widely used method. Naegele's rule adds 280 days (40 weeks) to the first day of your last menstrual period. This assumes a 28-day cycle with ovulation on Day 14. It is the standard method used by most Australian obstetricians and midwives.
Method 2: Conception Date
If you know when you conceived (e.g. through ovulation tracking or IVF), the calculator adds 266 days (38 weeks) to that date. Note that the LMP method is actually measuring from 2 weeks before conception, which is why the total is 280 days vs 266 days.
Method 3: Ultrasound — Most Accurate
An early ultrasound (ideally at 8–12 weeks) is the most accurate way to confirm gestational age and due date. Enter your scan date and the gestational age your sonographer noted. The calculator works back to find your adjusted LMP and calculates the EDD from there.
What Is Gestational Age?
Gestational age is measured in weeks and days from the first day of the LMP, not from the date of conception. At the time of a missed period, you are already about 4 weeks pregnant by this measure. A full-term pregnancy is typically between 37 and 42 weeks gestational age.
Frequently Asked Questions
How accurate is an estimated due date?
The EDD is an estimate. Only about 5% of babies are born on their exact due date. Most births occur within 2 weeks either side. Early ultrasound (before 13 weeks) is the most accurate way to set a due date, as it can correct for irregular cycles.
What week does each trimester start?
The first trimester is weeks 1–13. The second trimester is weeks 14–27. The third trimester is weeks 28–40 (or delivery). Trimester boundaries can vary slightly by source; these are the most commonly used definitions in Australia.
What is full term?
A baby born at 37–40 weeks is considered early full term or full term. Babies born at 41–42 weeks are late term. Full term is associated with the best outcomes for feeding, breathing, and brain development.
My cycle is not 28 days — will this affect the due date?
Yes. Naegele's rule assumes a 28-day cycle. If your cycle is longer (e.g. 35 days), ovulation likely occurred later, so the EDD calculated from LMP may be about a week later than your actual due date. An early ultrasound will give a more accurate result for irregular cycles.
What is the difference between gestational age and fetal age?
Gestational age is counted from the LMP (adds ~2 extra weeks at the start). Foetal age (or embryonic age) is counted from conception. A 10-week gestational age baby has a foetal age of about 8 weeks. Doctors always use gestational age in practice.
How do I use the Period Calculator with this tool?
Use our Period Calculator to predict when you are likely to ovulate and identify your fertile window. Then use this Pregnancy Due Date Calculator once a positive pregnancy test confirms your pregnancy.
Related Health & Pregnancy Calculators
Period Calculator
Next period, ovulation and fertile window
Gestational Age Calculator
Pregnancy due date and gestational age
Age Calculator
Calculate age in years, months, days
Date Calculator
Add or subtract days, date difference
Biological Age Calculator
Biological vs chronological age