Yes, it is possible to get pregnant from having sex just once. When calculating your potential pregnancy date, you should consider the date of your last period (April 20) as well as the date of intercourse (May 2). The most fertile time for conception is typically around ovulation, which usually occurs about two weeks after the start of your last period. However, sperm can survive inside the female reproductive system for up to five days, so if you had sex close to ovulation or during this fertile window, there is a chance of pregnancy. To determine a more accurate estimate, it is recommended to consult with a healthcare professional or use an ovulation calculator that takes into account your menstrual cycle length and other factors.