The Pregnancy Due Date Calculator is an essential tool in obstetric care, providing an estimate of when a baby is likely to be born. The most widely used method for estimating the due date is based on Naegele’s Rule, which calculates the EDD as 280 days (40 weeks) from the first day of the last menstrual period (LMP). This assumes a regular 28-day menstrual cycle, with ovulation occurring around day 14.

While LMP-based dating is simple and commonly used, it has limitations, especially if menstrual cycles are irregular or if the exact LMP date is uncertain. In such cases, early pregnancy ultrasound is a more reliable method, as it provides gestational dating based on fetal measurements. Ultrasound dating in the first trimester is considered the most accurate and can be used to adjust or confirm the due date calculated from the LMP.

Accurate estimation of the due date is critical for guiding prenatal care, timing of screening tests, and planning for delivery. It helps clinicians anticipate potential complications, such as post-term pregnancy, and decide when interventions like induction of labor may be appropriate. At the same time, it is important to remember that the due date is only an estimate, only about 5% of women deliver exactly on their calculated due date. Most births occur within a two-week window before or after the EDD.