Nope, 40 weeks is the correct answer. Usually, the calculation is done from the first day of the last menstrual period, and from the medical point of view, we consider 40 weeks of pregnancy (even if doctors consider a period between 38 and 42 weeks a normal pregnancy). 40 weeks are exactly 280 days, that are ~9 months. So for this reason we say that the pregnancy is 9 months, but doctors usually say 40 weeks.