Investor.govThe U.S. Securities and Exchange Commission (SEC) Office of Investor Education “provides an introduction to markets and investing” to help you make sound investment decisions and avoid fraud. This site also contains calculators such as the Savings Goal Calculator - to help you plan purchases, and the Compound Interest Calculator that shows how much money you save if you leave your savings to earn compound interest. Compound interest definition: earning interest not only on the money that you are saving but also on the interest that you have earned.