# Interest Rate

## Definition

The term interest rate is used to describe the amount charged to borrow money.  It is the percentage of the principal paid by the borrower in each time period; typically stated as an annual rate of interest.

### Calculation

Interest Paid = Principal x (Interest Rate / Period) x Number of Periods

### Explanation

The rate of interest charged to borrowers can vary with the perceived credit risk, or risk of repayment.  Borrowers that present a higher risk of non-payment may be charged a higher rate of interest on a loan.

Interest rate is often confused with annual percentage rate, or APR.  The APR can be used to compare the total cost of a loan to alternatives.  The APR takes into consideration fees and mortgage points as well as the interest rate on the loan.  This relationship is demonstrated in the equation below:

APR = Interest Rate + Fees + Points

There are only three variables needed to determine the monthly payment on a loan:  interest rate, term, and principal amount.

### Example

Bill borrows \$1,000 from a local bank at a rate of 10% per year.  Bill only needs to borrow the money for six months.  The interest payment on this loan would be:

= \$1,000 x (10% / year) x 0.5 years
= \$1,000 x 0.10 x 0.5, or \$50

The effects of compounding can be witnessed using our compound interest calculator.