Use the Due Date Calculator During pregnancy, it is very important to know exactly your due date. Because it will help with preparation for delivery, nutritional counseling and knowing everything the mother and baby need after birth. There are many ways to calculate your due date, but the most common method is to use a due date calculator. This article explains how to use the due date calculator and how many weeks into your pregnancy is your due date? Step One: Using the Due Date Calculator First, visit any online due date calculator website. These websites offer easy-to-use calculators. Typically, you will need to enter the first day of your most recent menstrual period