You can calculate the month you conceived a baby by using the due date, according to BabyMed. BabyMed provides a conception calculator that allows you to enter your due date and get a five-day window of when you conceived.
The calculation is possible because women normally ovulate, and thus conceive, 14 days before their period due date, explains BabyMed. This calculation uses the standard 28-day cycle, which is normally what health care providers use to calculate a due date. Women with longer cycles typically ovulate after 14 days, and possibly deliver a few days after the estimated due date. It is possible for women to get pregnant from five to six days before ovulation.