Calculate your estimated due date (EDD) using three methods: Last Menstrual Period (with cycle length adjustment), conception date, or IVF transfer date. Shows trimester dates, key milestones, and a visual pregnancy timeline.
Select from three calculation methods: LMP (Last Menstrual Period) — the most common clinical method; Conception Date — if you know when conception occurred; or IVF Transfer Date — for Day 3 or Day 5 embryo transfers.
For LMP: enter the first day of your last period and your average cycle length (default 28 days). Longer cycles shift the due date later; shorter cycles move it earlier. For conception: enter the date. For IVF: enter the transfer date and embryo age.
Your estimated due date is shown prominently. The visual timeline shows your current position and the three trimesters. Key dates are listed: first prenatal visit, anatomy scan (week 20), glucose test (week 24–28), and third trimester start.
Naegele's Rule: add 280 days (40 weeks) to the first day of the last menstrual period. This assumes a 28-day cycle with ovulation on day 14. If your cycle is longer or shorter than 28 days, the due date is adjusted: for a 30-day cycle, add 2 extra days; for a 26-day cycle, subtract 2 days. This is because ovulation (and therefore conception) occurs around day 14 of a 28-day cycle — but the same day relative to your cycle end regardless of cycle length.
Only about 4–5% of babies are born exactly on their estimated due date. About 80% of births occur within 2 weeks either side of the EDD. The most accurate dating method is an early ultrasound (before 14 weeks), where crown-rump length measurement can estimate gestational age to within ±5–7 days. LMP-based dating is accurate to within ±2 weeks. Your healthcare provider may adjust the due date after your dating scan.
Gestational age counts from the first day of the LMP — typically 2 weeks before conception actually occurred. Fetal age (or embryonic age) counts from the actual date of fertilisation. A fetus described as "40 weeks gestational age" is approximately 38 weeks from conception. Healthcare providers universally use gestational age because the LMP is a known, consistent reference point, whereas the exact date of conception is rarely known with certainty.
For IVF, the embryo age at transfer is known precisely. Day 3 transfer: add 263 days to the transfer date (266 days from fertilisation minus 3 days already elapsed). Day 5 transfer (blastocyst): add 261 days to the transfer date (266 minus 5). The EDD is calculated as conception date + 266 days. IVF due date calculations are more accurate than LMP-based ones because fertilisation date is known exactly.
First trimester: weeks 1–13 (conception through week 13). Second trimester: weeks 14–27. Third trimester: weeks 28–40+. Each trimester represents roughly 13 weeks. The first trimester covers embryonic development and the highest-risk period for miscarriage. The second trimester is generally the most comfortable. The third trimester involves rapid fetal growth and preparation for birth.
Yes — ultrasound-based dating may revise the LMP-based EDD. ACOG guidelines recommend: if the first-trimester ultrasound EDD differs by more than 5–7 days from LMP, adjust to the ultrasound date. If the 14–20 week ultrasound differs by more than 10–14 days, adjust. After 20 weeks, ultrasound dating is less accurate and EDD is usually not revised unless there is a major discrepancy.
