An index is a financial table that is used by lenders and bankers to calculate the interest rates on adjustable mortgages or on treasury bills. Mathematical tables are simply a way for lenders to quickly see the difference between various interest rates. Index tables are essential for the lending industry because they provide a physical way for bankers to determine the different monthly payments and profits that are associated with a particular interest rate. Indexes are very similar to amortization tables and are often used by home buyers and lenders to see the change of mortgages based upon interest differences. Tables graphically show the different interest percentage points and the amount that this will raise a particular mortgage. An index is a chart of numbers that shows the different interest rates that are associated with a particular loan or home mortgage.