Compound Interest Calculator

Simple interest is calculated only on the original principal amount. Compound interest is calculated on the principal plus any previously earned interest, so your money grows exponentially. For example, $1,000 at 5% simple interest earns $50/year forever, while compound interest earns more each year because interest earns interest.

More frequent compounding produces slightly higher returns because interest is calculated and added to the principal more often. For example, $10,000 at 5% for 10 years yields $16,288.95 with annual compounding, $16,386.16 with monthly, and $16,487.21 with daily compounding. The difference grows with higher rates and longer time periods.

The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual interest rate to get the approximate number of years. For example, at 6% interest, your money doubles in roughly 72/6 = 12 years. It works best for rates between 4% and 12%.

Start investing as early as possible to give compounding more time to work. Choose investments with higher interest rates when appropriate for your risk tolerance. Select accounts with more frequent compounding (monthly or daily over annually). Reinvest all earnings rather than withdrawing them, and make regular additional contributions.

The formula is A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is the number of compounding periods per year, and t is the number of years. With recurring contributions, each deposit also compounds for the remaining time, which this calculator handles by simulating each compounding period.