Pregnancy Calculator

From the first day of the last menstrual period, estimate the due date, how far along the pregnancy is today, and the current trimester.

Dates

First day of last period

Average cycle length (days)

Result

Pick the date and press Calculate.

How the estimate works

The due date is set 280 days (40 weeks) after the last period, shifted by how much the cycle differs from 28 days. Only about 1 in 20 babies arrives on the due date itself — full term spans weeks 37 through 42 — and an ultrasound dating scan is more accurate, so treat this as an estimate to discuss with a clinician.