Annual Percentage Rate (APR) measures how much a loan or other line of credit costs you in interest over one year, and it is expressed as a percentage of the total amount of money that you borrow.
To work out the APR, take the amount of your loan and how much interest you will be charged over one year and divide that interest amount by the amount of your loan. Multiply the number by 100 and you get your APR. For example, you borrow £1,000 and are charged £180 in interest for that year. The APR is calculated like this:
180/1000 x 100 = 0.18 x 100 = 18%
Normally you know what the APR is before you know how much the interest you will be charged is, so you can determine how much your interest over the course of a year is by using this formula:
1000 x 18% = 180