Pregnancy Due Date Calculator

The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). Alternatively, add 9 months and 7 days to your LMP. This assumes a 28-day menstrual cycle with ovulation on day 14.

Only about 4% of babies are born exactly on their due date. About 80% of births happen within 2 weeks before or after. The due date is a target, not a guarantee. Ultrasound dating in the first trimester (8–13 weeks) is the most accurate method.

Naegele's Rule assumes a 28-day cycle. If your cycle is longer (e.g., 35 days), ovulation happens later, so add the extra days to the due date. If your cycle is shorter (e.g., 21 days), subtract days. Our calculator adjusts for cycle length automatically.

First trimester: Weeks 1–13 (months 1–3). Second trimester: Weeks 14–26 (months 4–6). Third trimester: Weeks 27–40 (months 7–9). The second trimester is often the most comfortable with reduced nausea and increased energy.

Full term is defined as 39–40 weeks of pregnancy. Early term is 37–38 weeks. Late term is 41 weeks. Post-term is 42+ weeks. Babies born before 37 weeks are considered premature (preterm). Medical intervention is usually considered after 42 weeks.

Gestational age is counted from the first day of your last menstrual period (LMP), not from conception. So at the time of conception (around week 2–3), you are already considered 2–3 weeks pregnant. A full-term pregnancy is 40 weeks gestational age.

Ovulation and conception typically occur around day 14 of a 28-day cycle — about 2 weeks after the LMP. So the conception date is approximately LMP + 14 days. Gestational age is measured from LMP, not conception, which is why a full-term pregnancy is 40 weeks from LMP but ~38 weeks from conception.

Yes. If you know the conception date, add 266 days (38 weeks) to get the estimated due date. Our calculator supports this: switch to Conception Date mode and enter the date.

Week 4–5: Positive pregnancy test. Week 6–8: Heartbeat detectable on ultrasound. Week 10–12: First trimester screening. Week 18–20: Anatomy scan/gender. Week 24–28: Glucose screening. Week 36–40: Weekly check-ups, baby positions confirmed, cervix checks.

For IVF pregnancies: if a 3-day embryo transfer was performed, add 263 days (38 weeks − 3 days) to the transfer date. For a 5-day blastocyst transfer, add 261 days (38 weeks − 5 days). Our calculator handles IVF transfer date mode as well.