Pregnancy Due Date Calculator

The standard method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). For cycles other than 28 days, ovulation occurs earlier or later, so the due date shifts by the same number of days. Ultrasound dating in the first trimester is more accurate and is typically used to confirm or adjust the LMP-based estimate.

LMP-based due date calculators are accurate within about 5–7 days for women with regular 28-day cycles. For irregular cycles, accuracy decreases. Only about 5% of babies are born on their exact due date — most arrive within a 2-week window. First-trimester ultrasound (at 8–12 weeks) is the gold standard for dating accuracy.

Gestational age counts pregnancy from the first day of your last period, not from conception. This means gestational age at birth is typically 40 weeks, even though the embryo is only about 38 weeks old from fertilisation. Healthcare providers use gestational age universally because the exact date of conception is rarely known.

This calculator adjusts for cycle length by shifting ovulation timing. If your cycles vary widely (by more than 5–7 days cycle to cycle), the LMP method is less reliable. In this case, an early ultrasound is the best way to establish an accurate due date. Irregular cycles are common — use our ovulation calculator to identify your fertile window more precisely.

A pregnancy is considered full term from 39 weeks 0 days to 40 weeks 6 days. Early term is 37–38 weeks; late term is 41 weeks; post-term is 42 weeks or beyond. Babies born before 37 weeks are considered premature (preterm). The weeks 37–42 are all within the normal range for delivery.

For IVF pregnancies, due dates are calculated differently — typically 266 days (38 weeks) from the egg retrieval date, or adjusted based on the embryo transfer day (day 3 or day 5 transfer). This calculator uses LMP-based dating, which is not appropriate for IVF. Use the dates provided by your fertility clinic.

Early signs include missed period, nausea (morning sickness), breast tenderness, fatigue, frequent urination, and light spotting (implantation bleeding). A home pregnancy test can detect hCG hormone from around the time of a missed period. Always confirm with a healthcare provider for a clinical diagnosis.

Most healthcare providers recommend booking your first prenatal appointment at 8–10 weeks of pregnancy. In the UK, the first midwife booking appointment is typically at 8–10 weeks with a dating scan at 11–14 weeks. In the US, the first OB visit is usually at 8 weeks.

If your last period started 6 weeks ago today, you are approximately 6 weeks pregnant (gestational age). In terms of fetal development, the embryo is about 4 weeks old (fertilisation occurs around week 2 of the gestational count). At 6 weeks, a heartbeat may be detectable on ultrasound.

EDD stands for Estimated Delivery Date — it is the due date. The terms are interchangeable. 'Estimated' is key: it is a statistical midpoint, not a deadline. Labour can naturally start anywhere from 37 to 42 weeks gestation, and only about 1 in 20 babies arrives on their exact EDD.

Yes, and this is common. If the ultrasound dating differs from your LMP-based estimate by more than 5–7 days, most clinicians will adjust the official due date to the ultrasound measurement. This is because LMP-based dates assume a 28-day cycle with ovulation on day 14, which doesn't apply to everyone.