You have paid all your Christmas presents with your credit card and have trouble paying for the whole bill this month. You decide to wait for next month to pay for the remaining amount. What will happen? You will pay more because the bank will charge you interest. Why do you have to pay interest? You have bought items that you can use now and pay one month or two months later. Through your credit card, your bank has lent you money. This ability to use something before paying for it has a price: interest. Interest is not always at your expense. You can earn interest on saving. If you open a saving account, for example, you commit to leave a minimum amount in the account. In return, the bank will pay you an interest.