Congratulations on your new pregnancy! One of the first things a women usually does in her first trimester is to figure out her estimated due date. You can use a similar technique your health care provider will use to figure out your estimated due date, or EDD. A doctor or midwife will figure your initial EDD, by figuring from your last normal menstrual period (LNMP). They will take the first day of your last period and add 266 days (or 38 weeks) to figure your estimated due date. This gives an estimate of your due date but it isn’t 100%