Pregnancy Due Date Calculator

Estimating your due date

This calculator estimates your due date using Naegele’s rule, the standard method used in maternity care. It takes the first day of your last menstrual period (LMP), adds about 280 days (40 weeks), and adjusts for your average cycle length. It also estimates your current gestational age in weeks and days, your trimester, and the days remaining.

Gestational age is counted from the first day of your last period, not from conception, which is why a “40-week” pregnancy is really about 38 weeks from conception. The calculator follows the same convention your provider uses, so the numbers line up with clinical milestones.

If your cycle isn’t 28 days

The classic formula assumes a 28-day cycle. If yours is longer or shorter, enter your average length and the estimate shifts accordingly — a longer cycle generally means a slightly later due date.