how long is a pregnancy
A pregnancy is suppose to last 40 weeks but not really because they add the 2 weeks between your LMP and your conception date. It's weird, so actually it's 38 weeks. P.S. Never count the months... counting by the week is way more acurate.
The only time you might want to be concerned if it is more than a month either way. Full term pregnancy is bettween 37-40 weeks not exactly 40 weeks. If you have a baby at 37 weeks they still consider it full term. You're due date is at 40 weeks and 37 is considered full term. But there is only one month with exactly 4 weeks(most years) so it still is about 9 months.