John – My dad wants to add me to his mortgage loan. Will that screw up my credit? I’m 21.

Answer – It doesn’t matter if you’re 21 or 121, what your dad is suggesting is a horrible idea. When your name goes on the loan you’ll become just as liable for the debt as he is. It’s also going to screw up your debt to income ratios and that will come back to haunt you when you want to apply for a mortgage someday. If he wants to do this to help you build credit then suggest that he add you as an authorized user on one of his credit cards.