How is a Due Date Calculated?
Doctors typically estimate a due date based on the First Day of your Last Menstrual Period (LMP). This is known as Naegele's Rule.
The standard pregnancy lasts about 280 days (or 40 weeks) from the LMP. However, only about 4% of babies are born on their exact due date. Most are born within two weeks before or after.
Cycle Length Matters
The standard calculation assumes a 28-day cycle with ovulation occurring on day 14. If your cycle is longer (e.g., 32 days), ovulation likely happened later, meaning your due date will be pushed back slightly. Our calculator automatically adjusts for this.