Knowing the interest rate that you are being charged is vital for making wise financial decisions. If market interest rates fall, it may be worth the time and closing costs of refinancing your loan, especially if it is a larger loan such as a mortgage or if rates have dropped significantly. The interest rate being charged is dependent on the amount you owe and the amount of interest. The interest rate being charged can be calculated the same way for credit cards, mortgages and other loans.

Check your loan statement to find out how much interest you paid and the total amount remaining on your loan. The interest charged may be listed as "Interest Charged" or "Interest." The amount still owed will be listed as "Principal" or "Outstanding Balance."

Divide the interest paid by the amount owed to find the periodic rate. For example, if you paid $123.75 when you owe $8,250, you would divide $8,250 by $123.75 to get 0.015.

Multiply the periodic rate by the number of periods each year to find the annual interest rate. In this example, the interest was charged quarterly, you would multiply 0.015 by 4 to get 0.06, or a 6 percent annual interest rate.