How to Calculate Due Date
In order to calculate your due date, you'll need to know either the date of conception or the date of your last menstrual cycle. The due date will be 40 weeks after the first day of your last menstrual period (LMP) or 38 weeks after the date of conception. To make things simpler, use a due date calculator like the one like this one.
How Pregnant Am I?
Hopefully I haven't already confused you, but to calculate which month or trimester you are in, use this handy chart.