Qualifications to recieve a mortgage loan

[Luke Pastore]

I am 20 years old, still in college, but I am beginning to look into purchasing a duplex, living in one part and renting the other. It seems like the most logical place to start my real estate investing, given the ability to apply for an FHA loan due to my circumstances. I have been an authorized user on my parents credit card for about 4 years to begin building my credit and I just received my first independent credit card. I know my job now is to continue to build my credit and to continue working. I had an internship that is now a part time job that I will have had all summer and will have through the school year. I have read places that to apply for the FHA loan, most banks require you to have 2 or even 3 lines of credit and most people online recommend getting and paying off two or more credit cards for a few months before looking for a loan.

Would my authorized user card be considered a second card or should I consider a third credit card separate from that? It seems a bit much to simply continue to build credit but I am new to this so I could be wrong!