Albert Einstein reportedly called compound interest the eighth wonder of the world. Whether he actually said it or not, the math backs up the awe. Compound interest is interest earned on interest. When you invest money, you earn a return. When you leave that return invested, it also earns a return. Over time, this creates a snowball effect that is genuinely staggering. Here's a simple example. Suppose you invest $10,000 at an average annual return of 7%. After 10 years: ~$19,