How firm is your estimated due date?
An estimated due date (EDD) is calculated the same way whatever the source — 40 weeks of pregnancy — but how much it can be trusted depends on where it came from. This calculator gives your EDD and, alongside it, a plain explanation of how firm that date is for the method you chose.
| Dating method | How firm |
|---|---|
| IVF transfer | Very firm — the embryo’s age is known exactly |
| Ultrasound before 14 weeks | Firm — typically within about 5–7 days |
| Last menstrual period | Good with regular cycles and a certain date; may be revised by an early scan |
| Conception date | Good if ovulation was tracked; less so from an intercourse date alone |
| Ultrasound after 20 weeks | Less firm for dating — babies grow at different rates |
Estimated, not expected
Even a perfectly dated pregnancy rarely ends on the EDD. It marks the middle of a window: most babies are born between 37 and 42 weeks. The calculator shows the date full term begins (39 weeks) and the end of 41 weeks, by when most babies have arrived.
Learn more
Our guide How Accurate Is a Due Date? explains why dates are adjusted, and the EDD Calculator Pregnancy applies the redating rule to your own period and scan dates.