The Naegele’s Rule Calculator is a tool used to estimate the due date of a pregnancy based on the first day of the last menstrual period. By entering this date, the calculator adds 280 days (or 40 weeks), which is the average length of a pregnancy, to determine the estimated due date. This helps expectant parents plan and prepare for the arrival of their baby. The simple process makes it an essential tool for anyone wanting a quick and reliable due date estimate.