A compound interest calculator helps calculate how much an investment or savings will grow over time by earning interest on both the initial principal and the accumulated interest. It uses the formula A=P(1+rn)ntA=P\left(1+\frac{r}{n}\right)^{nt}A=P(1+nr​)nt, where AAA is the amount after time ttt, PPP is the principal amount, rrr is the annual interest rate, nnn is the number of times interest is compounded per year, and ttt is the time in years. Using the calculator, you input the starting amount, interest rate, the length of time the money will be invested or saved, how often interest compounds (daily, monthly, quarterly, annually), and any additional contributions. The calculator then shows the total balance at the end, the interest earned, and the effect of compounding frequency. For example, a $10,000 deposit at 4% interest compounded daily grows more over time than if compounded annually. Several online tools such as NerdWallet, Bankrate, and SoFi have free compound interest calculators that allow users to experiment with different scenarios to plan savings or investments effectively.