Due Date Calculator

How the Due Date Calculator Works

The standard due date is 40 weeks — 280 days — from the first day of your last menstrual period (LMP). This is Naegele’s rule, and it’s how most providers set an initial due date. If you know your conception or IVF transfer date instead, the calculator counts 266 days from there, since conception happens about two weeks after your period starts.

Because ovulation timing depends on your cycle, the calculator lets you adjust for a cycle longer or shorter than the average 28 days. It also shows your estimated conception date, how far along you are today, your trimester, and how many days remain. Only about 1 in 20 babies actually arrives on the due date — most come in the two weeks either side.

due date = last period + 280 days  (or conception + 266 days)

Note: these are estimates based on standard averages. Every pregnancy is different — your doctor or midwife, using an ultrasound, gives the most accurate dates.