Using a pregnancy test calculator is easy and simply requires inputting individual data including the date of the woman's last period as well as the typical length of the menstrual cycle, reports WebMD and BabyMed. Pregnancy test calculators can be found on those websites.
Women who keep track of their ovulating schedules can also find out their date of impregnation or fertilization on their own. They can do this by first taking their last day of menstruation, adding 40 weeks to determine their baby's due date and then subtracting 266 days to get the date that they became pregnant according to WebMD and BabyMed. Women are impregnated during the ovulation period and for most women, the ovulation period follows a schedule so it can be tracked at home. It is possible for a woman to know when she is ovulating by watching for a slimy secretion that typically occurs just before ovulation, writes Mayo Clinic.
It is also possible to visit a doctor for an ultrasound. During the ultrasound, the doctor will be able to determine when the baby was most likely conceived based on signifiers, such as the baby's heartbeat, reports BabyMed. A baby's heart beat begins to be audible on an ultrasound around the 6th week, for example, so doctors know that a baby whose heartbeat is audible is 6 weeks or older.