Compound Interest Calculator
Calculate how your investments grow over time with the power of compound interest. Enter your initial investment, monthly contributions, expected return rate, and time horizon to see how your money can grow.
Understanding Compound Interest
Compound interest is one of the most powerful concepts in finance. Unlike simple interest, which is calculated only on the initial principal, compound interest is calculated on the principal plus all previously accumulated interest. This means your money grows exponentially over time — often called the "eighth wonder of the world."
The Compound Interest Formula
The basic formula is: A = P(1 + r/n)^(nt), where A is the future value, P is the principal, r is the annual rate, n is the compounding frequency, and t is the time in years. With regular contributions, the formula becomes more complex but the principle remains the same.
Key Factors That Impact Your Returns
- Starting early: Time is the most important factor. Starting 10 years earlier can double or triple your final balance.
- Consistent contributions: Regular monthly deposits dramatically accelerate growth through dollar-cost averaging.
- Compounding frequency: More frequent compounding (daily vs. annually) yields slightly higher returns.
- Rate of return: Even small differences in annual returns compound into major differences over decades.
How to Use This Calculator
Enter your initial investment amount, how much you plan to contribute each month, your expected annual return rate (the S&P 500 has historically returned about 7% after inflation), your preferred compounding frequency, and the number of years you plan to invest. The calculator will show your projected future value, total contributions, total interest earned, and a visual growth chart.