A compound interest calculator is a tool that helps individuals determine how much interest will be earned on an investment over time. It takes into account the principal amount, the interest rate, and the frequency of compounding, which can be annually, semi-annually, quarterly, or monthly. By inputting these values, users can see how their money grows over time. These calculators are useful for planning savings and investments, as they provide a clear picture of potential future earnings. Many online platforms and financial institutions offer free compound interest calculators, making it easy for anyone to estimate their financial growth.