Pregnancy Due Date Calculator

How it works

A pregnancy due date — the estimated date of delivery (EDD) — is most commonly calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). This rule assumes a 28-day cycle with ovulation on day 14, which makes the actual fertilization event approximately 14 days after the LMP, so the embryo is technically about 38 weeks old at delivery even though we count 40 "weeks of gestation".

This calculator computes both the due date and your current gestational age (in weeks and days), and tells you which trimester you're in. The first trimester runs through week 12, the second from week 13 to week 26, and the third from week 27 to delivery.

Important: the calculated EDD is an estimate. Only about 4% of babies are born on their exact due date. Around 80% are born within the two weeks before or after, and "term" delivery is anywhere from 37 to 42 weeks. Earlier than 37 weeks is preterm; after 42 weeks is post-term and providers usually recommend induction.

For more accurate dating, providers use ultrasound measurements during the first trimester, particularly the crown-rump length at 7–13 weeks, which is accurate to within ±5–7 days. Later ultrasounds become progressively less accurate for dating because growth varies between fetuses.

If your cycle is not 28 days, your conception likely occurred later (long cycle) or earlier (short cycle) than Naegele's rule assumes. IVF pregnancies are dated from the embryo transfer date rather than LMP. Always discuss your specific dating with your obstetrician or midwife — this calculator is for general informational use only and is not a substitute for prenatal care.