Many mortgage payments are made up of four parts, called PITI. PITI is an acronym that stands for principal, interest, tax, and insurance. It's important to understand PITI because it is the real number you need to use in order to find out how much mortgage you can afford to pay each month. One of the biggest mistakes first-time homebuyers make is using only the principal plus interest figure to calculate how much they'll be paying every month for their mortgage. Then, when the lender comes back and denies them, the prospective buyer is confused. Knowing and understanding PITI will…