What is a pregnancy cycle calculator? A pregnancy cycle calculator is a tool that helps women calculate their pregnancy cycles and predict their due date. By inputting the date of a woman\’s last menstrual period, the computer will automatically calculate important information such as the pregnancy cycle and due date, and provide feedback to the user. This tool can be of great help to women both during and during pregnancy. How to use the pregnancy cycle calculator. To use the pregnancy cycle calculator, the first step is to enter the date of your last menstrual period. At the same time, you need to pay attention to if you have irregular menstrual cycles.