How to Use the Compound Interest Calculator
Our free compound interest calculator helps you estimate how your investments will grow over time. Simply enter your initial deposit, monthly contribution, expected annual return, and investment period. The calculator instantly shows your final balance, total interest earned, and total amount invested.
- Enter your initial amount — the lump sum you're starting with.
- Set your monthly contribution — how much you'll add each month.
- Choose an annual interest rate — a conservative estimate based on historical market returns.
- Select your investment horizon — the number of years you plan to invest.
- Click "Calculate Growth" to see your results and a visual growth chart.
The Power of Compound Interest
Albert Einstein reportedly called compound interest the "eighth wonder of the world." When you earn interest on your interest, your money grows exponentially rather than linearly. The longer your investment horizon, the more dramatic the compounding effect becomes. Starting early and contributing consistently are the two most powerful levers you can pull.
Compound Interest Formula
Our calculator uses the standard compound interest formula: A = P(1 + r/n)^(nt) + PMT × [((1 + r/n)^(nt) - 1) / (r/n)], where P is the principal, r is the annual interest rate, n is the compounding frequency (monthly), t is the time in years, and PMT is the monthly contribution.
Frequently Asked Questions
What is a good annual return rate? Historically, the S&P 500 has returned about 7-10% annually before inflation. For conservative planning, use 5-7%.
How does compounding frequency affect growth? More frequent compounding (daily vs. yearly) results in slightly higher returns. Our calculator compounds monthly, which is standard for most investment accounts.
Should I include inflation? For a more realistic picture, subtract your expected inflation rate from your expected return. For example, if you expect 7% returns and 3% inflation, use 4% as your rate.