What Week & Month Am I In?

Even if this isn't your first pregnancy, figuring out what week or month you are in and what your due date is can be very confusing. Pregnancy is a total of nine months, ten lunar months or 40 weeks total and is pretty much calculated four total weeks to each month. With my own pregnancy I tried calculating four weeks to a month to figure out my due date but it didn't add up and that's when I found out I was adding up what is called the Lunar month calculation. I've done some research and found that the:

First Month of pregnancy is 1-5 weeks,
Second Month is 6-9 weeks
Third Month is 10-13 weeks
Fourth Month is 14-18 weeks
Fifth Month is 19-22 weeks
Sixth Month is 23-27 weeks
Seventh Month is 28-31 weeks
Eighth Month is 32-36 weeks
Ninth Month is 37 -40 weeks

It's a confusing type of calculation but its basically what doctor's use. The way you start and end your pregnancy week is say conception occurred on Tuesday the 6th of October. Your first week of pregnancy started on that Tuesday the 6th and ends the next Tuesday which would be the 13th of October and your second week of pregnancy begins on the 14th.

Here is a better explination from BabyCenter's Site:

Why are you telling me I'm 4 weeks pregnant when I'm in my 5th week?
Why are you telling me I'm 4 weeks pregnant when I'm in my 5th week, counting from the first day of my last period?

This is a pretty confusing issue for a lot of pregnant women. The fact is when you're in your 5th week of pregnancy, you are 4 weeks pregnant! During the week you start your period, you are in your first week of pregnancy, but you have not yet completed any weeks so you are zero weeks pregnant. Think about it this way you don't say that a baby is one year old during his first year of life do you? He is not considered to be one year old until he's actually in his second year.

A lot of pregnancy books and web sites don't make this distinction, which makes things even more confusing. To make things as simple as possible, we recently standardized our wording so that we only refer to you as being a certain number of weeks pregnant. We try not to say "you are in your 5th week" because that's when you are actually 4 weeks pregnant. We just say, "you are 4 weeks pregnant." You'll notice that the weeks on our Pregnancy Calendar (and everywhere else) say "5 weeks" for example, not "week 5." And that's how most practitioners express it, too. If you start thinking in terms of how many weeks pregnant you are instead of what week you're in, you'll be less confused.

In order to really calculate what month you are in you will either need to wait until your first prenatal appointment so your doctor can confirm what week you are in. Or you can check the page titled When Is My Due Date? If you know when the first day of your last period.