You deposit $5,000 into a savings account earning 4% interest. After one year, you have $5,200. Pretty straightforward, right? But what if you leave it for 30 years? What if the bank compounds your interest daily instead of annually? What if you add $100 every month? The math gets complicated fast. Interest earns interest. That earned interest earns even more interest. The numbers accelerate in a way that feels almost magical—but it is just mathematics. You could try to calculate it year by year, by hand. Or month by month. But this is tedious and error-prone, especially when the compounding happens daily (365 times per year) and you are trying to predict 20 or 30 years into the future. Or you could use a compound interest calculator to instantly show that your $5,000 investment at 4% compounded daily will become $7,460 in 20 years—earning you $2,460 in completely passive growth. A compound interest calculator computes how your money grows when interest is added to your account repeate...