Due Date Calculator
Naegele's Rule Pregnancy Dating

The 280-day convention dates to the 1800s and still anchors modern obstetrics. It counts 40 weeks from the last menstrual period — not from conception, which typically happens about two weeks later. This calculator applies Naegele's rule with a cycle-length adjustment, the same approach used on standard pregnancy wheels.

A Window, Not a Deadline

The estimated date is the statistical center of a distribution. First pregnancies tend to run slightly longer, and normal deliveries span weeks 37 through 42. Use the date to plan — prenatal visits, screening windows, leave — while holding the actual day loosely.