Expecting parents often wonder, “When will my baby arrive?” A due date is usually estimated using a simple method called Naegele’s Rule. This calculation starts from the first day of your last menstrual period (LMP), adds 280 days (40 weeks), and then adjusts for your average cycle length. Because ovulation and conception typically occur about two weeks after the LMP in a standard cycle, this method gives a quick way to project the most likely delivery date. While this calculation is widely used by doctors, it’s important to remember that it provides an estimate, not a guarantee. Fewer than 5% of babies are actually born on their exact due date, with most arriving within a two-week window before or after. Your doctor may refine the estimate based on early ultrasounds, which can sometimes provide a more precise measurement. Use this calculator as a helpful guide, and always confirm timing and prenatal care details with your healthcare provider.