Pregnancy Due Date Calculator

The due date is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). If you enter a conception date instead, the calculator subtracts 14 days to estimate the LMP and then applies the same formula.

Naegele's rule assumes a 28-day menstrual cycle with ovulation on day 14. It is a widely used estimation method, but only about 4% of babies are born on their exact due date. Most births occur within one to two weeks before or after the estimated date.

The first trimester spans weeks 1 through 12 and involves major organ development. The second trimester covers weeks 13 through 26 and is when fetal movement becomes noticeable. The third trimester runs from week 27 until birth (around week 40) and focuses on growth and maturation.

A pregnancy is considered early term at 36 weeks and full term starting at 37 weeks. Babies born between 37 and 42 weeks are generally considered to have reached full-term development. Births before 37 weeks are classified as preterm.