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 Interest Rate is a finance charge expressed as an annual rate without the addition of other fees which must be included with the A.P.R.

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.

While it's designed to make it easier to compare loans, it's sometimes confusing because the A.P.R. includes some, but not all, of the various fees and charges that accompany a mortgage.  A.P.R.s can vary from lender to lender and loan to loan.

So, A.P.R.s are at best inexact. The lesson is, that A.P.R. can be a guide, but you need a mortgage professional to help you find the truly best loan for you.