Q: I looked at the pregnancy due date calculator why does it say 20 weeks but 18 weeks from conception? Did I conceive 20 weeks ago or 18 weeks ago? I am SO confused!
A: Due dates may seem confusing because women think pregnancy is 9 months (equal to 36 weeks) when actually we calculate pregnancy from the first day of your last period making it 10 months or 40 weeks. Therefore, by our calculations you are "pregnant" for a month before you miss your period and realize it. Since most women ovulate and conceive 2 weeks after their period you are technically "with child" for 9.5 months or 38 weeks. Your due date is most accurately calculated by the first day of your last menstrual period and your earliest ultrasound.