Is a womans pregnancy due date the same day she has sexual intercourse 9 months earlier? weird question i know, but just curious.

No, not quite: The counting of "weeks of pregnancy" or "gestational age" is standardized so that all doctors, nurses, and patients can talk about it the same way. The start date of a pregnancy is the first day of the menstrual period just before the pregnancy. That means ovulation & fertilization happen about 2 weeks after the start date of "the pregnancy". When intercourse happens doesn't affect the start date.