A Word About Due Date and Trimesters

After you announce your pregnancy, the first question that you will probably hear is "When is the Due Date?"

At your first prenatal visit, you doctor will help you to determine an expected delivery date (EDD). Your EDD is 40 weeks from the first day of your last menstrual period (LMP). If you deliver on EDD, your baby is actually only about 38 weeks old - because you egg didn't become fertilized until about 2 weeks after the start of your last menstrual period.

You can calculate your Due Date here: Your Due Date
If you search on the internet you will find quite a lot of calculators but I prefer this one because I think it's the best.
This cool calculator will give you quite a lot of information (not just your Estimated Due Date) but also info about the stage of pregnancy that you are in, baby status (size, weight, heartbeat), trimester stages, prenatal testing dates, timeline of significant milestones in your baby's development (when the baby can see the light, when you'll first start to feel how your baby is moving, when it can hear the sound etc.)

However, it's important to remember that your due date is only an estimate and that most babies are born between 38 and 42 weeks from the first day of their mom's LMP and only small percentage of women actually deliver on their due date.

Another common term that you will hear throughout your pregnancy is trimester. 
A pregnancy is divided into 3 trimesters:

1st trimester (from week 1 to the end of the week 12)
2nd trimester (from week 13 to the end of the week 26)
3rd trimester (from week 27 to the end of the pregnancy)