What is the difference between the interest rate and the A.P.R.?

You'll see an interest rate and an Annual Percentage Rate (A.P.R.) for each mortgage loan you see advertised. The easy answer to "why" is that federal law requires the lender to tell you both.

The A.P.R. is a tool for comparing different loans, which will include different interest rates but also different points and other terms. The A.P.R. is designed to represent the "true cost of a loan" to the borrower, expressed in the form of a yearly rate. This way, lenders can't "hide" fees and upfront costs behind low advertised rates.