Pregnancy Due Date Calculator

The standard estimated due date (EDD) is 40 weeks (280 days) from the first day of your last menstrual period (LMP) using Naegele's rule. If you know your conception date, IVF transfer date, or a scan-dated gestational age instead, this calculator works backwards from those to the same EDD. Only about 5% of babies are born on their exact due date — most arrive within two weeks either side.

EDD stands for Estimated Due Date — the date your baby is expected to arrive, calculated as 40 weeks from your last menstrual period. It is an estimate, not a deadline: a normal, full-term birth can happen any time from 37 to 42 weeks.

A first-trimester ultrasound (crown-rump length, ideally before 14 weeks) is the most accurate way to date a pregnancy and is what doctors use to confirm or revise the due date. LMP dating is reliable only if your cycles are regular and you remember the date. For IVF, the transfer date gives a very precise due date because the day of fertilisation is known.

First trimester: weeks 1–12. Second trimester: weeks 13–26. Third trimester: weeks 27–40. This calculator shows your current trimester, your week-by-week progress, and key appointment milestones such as the NT scan (11–13 weeks) and anomaly scan (around 20 weeks).

Gestational age is counted from the first day of your last period, not from conception — so you are already counted as about 2 weeks pregnant at the moment of conception. Enter your date above and the calculator shows your current weeks and days, your trimester, and how many weeks remain.

Yes. An early dating scan can move your due date if it differs from the LMP estimate by more than about a week. After the first trimester, the due date is usually kept fixed even though later growth scans estimate size, because early measurements date the pregnancy most accurately.

With irregular cycles, LMP-based dating is less reliable because the day of ovulation varies. Use the conception date or, better, an early ultrasound. This calculator lets you switch to those methods for a more accurate estimate.

The estimated due date is calculated the same way for twins, but twin and multiple pregnancies often deliver earlier than 40 weeks, and your obstetrician will plan delivery accordingly. Treat the EDD as a reference point, not a target.

Yes. It is completely free, needs no sign-up, and the calculation runs in your browser — your dates are not stored unless you choose to email yourself the result.