A constant (fixed) amount over an index that determines a lender’s yield on an adjustable rate loan. The interest rate of an adjustable rate loan is determined by adding a margin to an index. The size of the margin is typically a function of the index used and the credit worthiness of the borrower. Typical margins on a Prime Rate based loan would be 0.0 to 5.0 so that if the Prime Rate were 8.25% and the margin were 2.0 (typical for an “average” borrower), the interest rate would be 10.25% (8.25)