The first few months of pregnancy can be a really exciting time, and one piece of information that can feel particularly crucial is your due date. Pop culture has long portrayed pregnancy as a nine-month countdown to birth. But how long is pregnancy? Working this out can actually be a little bit more complicated than that.
“From a medical standpoint, doctors always talk in weeks and days,” says obstetrician, gynecologist (OB-GYN), and Flo medical board member Dr. Charlsie Celestine. “A full-term pregnancy is 40 weeks long, which equals 10 months. Yet commonly, people talk about pregnancy as being nine months long.”
Hang on. 10 months, not nine? How can that be the case? According to the National Health Service in the United Kingdom, the average length of human gestation is 280 days or 40 weeks, and that time starts from the first day of your last period, when you’re not technically pregnant yet. That’s because ovulation (which happens midway through your cycle) and fertilization haven’t occurred yet — but more on that later.