Sorry i just fixed my question, i had sex 5 days before my period suppose to start and i got pregnant, how do i calculate how long pregnant i am ?

Conception = 2 weeks: If you know the day, and there is no other possible day you could have become pregnant, use the day you had intercourse for the date of conception. It may be off by 24 hours or so but its a good estimate. By convention, conception occurs at 2 weeks of pregnancy. Its confusing but the convention is to use the first day of last period which is usually 2 weeks prior to conception. Best wishes!