Interest
For some loans, the amount actually loaned to the debtor is less than the principal sum to be repaid. This may be because upfront fees or points are charged, or because the loan has been structured to be sharia-compliant. The additional principal due at the end of the term has the same economic effect as a higher interest rate. This is sometimes referred to as a banker's dozen, a play on "baker's dozen" – owe twelve (a dozen), receive a loan of eleven (a banker's dozen). Note that the effective interest rate is not equal to the discount: if one borrows $10 and must repay $11, then this is ($11–$10)/$10 = 10 percent interest; however, if one borrows $9 and must repay $10, then this is ($10–$9)/$9 = 11-1/9 percent interest.Interest is the fee charged by the creditor to the debtor.Many conventions on how interest is calculated exist – see day count convention for some – while a standard convention is the annual percentage rate (APR), widely used and required by regulation in the United States and United Kingdom, though there are different forms of APR.
Interest rates may be fixed or floating. In floating-rate structures, the rate of interest that the borrower pays during each time period is tied to a benchmark such as LIBOR or, in the case of inflation-indexed bonds, inflation.
Interest is generally calculated as a percentage of the principal sum per year, which percentage is known as an interest rate, and is generally paid periodically at intervals, such as monthly or semi-annually.
