Glossary: Compound interest
This is effectively paying interest on interest. Interest is calculated not only on the initial sum borrowed (principal) or saved (see APR and AER) but also on the accumulated interest. The more frequently interest is added to the principal, the faster the principal grows and the higher the compound interest will be. Compound interest differs from “simple interest” in that simple interest is calculated solely as a percentage of the principal sum.
Where APR is the rate charged for money borrowed, Annual equivalent rate is how interest is calculated on money saved. The AER takes into account the frequency the product pays interest and how that interest compounds. So, if two savings products pay the same rate of interest but one pays interest more frequently, that account compounds the interest more frequently and will have a higher AER.
This is used to compare interest rates for borrowing. It is the total (or “gross”) interest you’ll pay over the life of a loan, including charges and fees. For credit cards where interest is charged at more frequent intervals, the APR includes a “compounding” effect (paying interest on interest). So for a credit card charging 2% interest a month (equating to 24% a year), the APR would actually be 26.82%.