[header] How to calculate effective interest rate [title] Familiarize yourself with the concept of the effective interest rate. [step] The effective interest rate attempts to describe the full cost of borrowing. It takes into account the effect of compounding interest, which is left out of the nominal or " stated " interest rate. 
[substeps] For example, a loan with 10 percent interest compounded monthly will actually carry an interest rate higher than 10 percent, because more interest is accumulated each month. The effective interest rate calculation does not take into account one-time fees like loan origination fees.