Gestational dating is a way of figuring out how many weeks pregnant someone is. It's a method that counts the weeks from the first day of their last menstrual period (LMP). Even though fertilization (conception - when the egg is fertilized by sperm) usually happens about two weeks after the LMP, gestational dating counts those two weeks as part of the pregnancy. So, if gestational dating says a person is is, for example, eight weeks pregnant, it means the actual time since fertilization is around six weeks. This method helps healthcare providers estimate the due date and track fetal development during pregnancy.