Exact date when your baby was conceived can not be calculated because it depends upon ovulation and day of intercourse. After the ovulation that usually occurs at mid of the cycle, egg can survive for 24 hours and sperms can live for 5-7 days after ejaculation in the female body. But some ladies can ovulate later and some earlier. So, sex 4-5 days before ovulation can result in pregnancy. So, when you ovulated and got pregnant is calculated by assuming that ovulation took place at mid of the cycle. That is why you can calculate conception date by adding 2 weeks in first day of last menstrual period.
