Roughly 5 months. Overall using the 'month' method is out dated at the drs and may even confuse people. Techically you are pregnant about 10 months, but they started saying 9 because you didn't realize until you were between 4-8 weeks. So when you are say due any day and you tell people you are 9 months, if you did the math
(due any day would be say 38-40 weeks) you would actually be 9 1/2 to 10 months. Make sense?