Compound Interest Calculator
See how your savings or investments grow over time with compound interest and regular monthly contributions, year by year.
Assumes a steady rate of return with no taxes, fees, or inflation. Real investment returns go up and down. For education, not financial advice.
| Year | Contributions | Interest earned | Balance |
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How it works
What is compound interest?
Interest that earns interest. Each period, interest is added to your balance, and the next period's interest is calculated on that larger balance. Over long periods this snowballs: at 7% a year, money roughly doubles every 10 years.
What's the formula?
For a single deposit: A = P(1 + r/n)ⁿᵗ, where P is the starting amount, r the annual rate, n the compounding periods per year, and t the years. With monthly contributions, this calculator adds each deposit and grows it month by month at the equivalent monthly rate for your chosen compounding.
Does compounding frequency matter much?
A little. More frequent compounding earns slightly more: $10,000 at 7% for 20 years is about $38,697 compounded annually and about $40,387 compounded monthly. The rate and the time invested matter far more.
What's the Rule of 72?
A quick shortcut: divide 72 by the interest rate to estimate how many years it takes to double your money. At 6%, it's about 12 years.