Gestational Age Calculator

Gestational age is counted from the first day of the last menstrual period (LMP) and is the standard way pregnancy is dated. Fetal age (conceptional age) starts from actual conception, which is about 2 weeks later. When your doctor says you're 8 weeks pregnant, the fetus is actually about 6 weeks old.

First trimester ultrasound (using crown-rump length) is the most accurate dating method, within ±3-5 days. After the first trimester, accuracy decreases. If ultrasound and LMP dates differ by more than 7 days, the ultrasound date is usually preferred.