Your Expected due date (EDD) or Expected date of confinement (EDC) can be calculated by various methods.
If you have a regular menstrual cycle of 28 days duration, then EDD is 280 days or 40 weeks from the first day of your last menstrual period (LMP). If you have a cycle of 30 days, than your ovulation occurs two days later and hence the due date also shifts further by 2 days.
If you know your precise date of conception (as may happen with IVF pregnancies), then the due date is calculated as 38 weeks from date of conception.
If your periods / cycles were irregular or you conceived within your lactation period and were not getting regular periods or soon after stopping your oral contraceptive pill, then it is not possible to calculate the EDD based on dates. The most accurate way to ‘date’ the pregnancy is to have an Ultrasound scan early in the pregnancy (between 6-12 weeks). The size of the fetus is measured and thus, the gestational age is estimated. Then, a program in the scan machines or computers can calculate the due date.
You can use our interactive Gestational Age Calculator and find out your due date by fixing the LMP arrow onto the date of the first day of your LMP. The wheel then tells you your EDD and also, how many weeks pregnant you are on a particular date.