What assumption is made when calculating EDD by LMP?

When calculating the Estimated Due Date (EDD) based on the Last Menstrual Period (LMP), it is typically assumed that ovulation occurs on day 14 of a regular menstrual cycle. This is grounded in the average cycle length of 28 days, where ovulation is expected to take place around the midpoint. This assumption is crucial because it helps health care providers estimate the timing of conception and the corresponding due date.

Understanding that ovulation is often considered to occur on day 14 allows for the application of standardized dating methods, making it easier to communicate due dates and monitor fetal development. Regularity of the cycle and patient recall of the last period do play significant roles in EDD calculations as well, but the critical assumption that connects the LMP to ovulation timing is that ovulation typically occurs around day 14.