Compound Interest Calculator
Enter a starting amount, monthly contribution, expected annual return and number of years to see how your money could grow — year by year.
Why compound interest is so powerful
Compound interest means earning returns on your previous returns. In the early years the effect looks small, but as the chart shows, the orange “growth” portion eventually overtakes the money you put in yourself. Read the full explanation in what is compound interest.
Time beats timing
Investing the same monthly amount for 30 years instead of 20 doesn’t give you 50% more — it often gives you roughly double. Starting early is usually more effective than chasing higher returns.
Pick realistic assumptions
Run an optimistic, a moderate and a cautious scenario. Remember that fees and taxes reduce returns, and that past performance doesn’t guarantee future results. Low-cost index funds are a popular way to keep costs down.
Frequently Asked Questions
What is the compound interest formula?
For a single deposit, Future Value = P × (1 + r)^n, where r is the periodic rate and n the number of periods. With regular contributions, each contribution also compounds for the time it is invested.
What is a realistic rate of return?
It depends on what you invest in. Savings accounts pay relatively little, while diversified stock portfolios have historically returned more over long periods but with significant ups and downs. Try several rates to see a range of outcomes.
Does this include inflation?
No. Results are in nominal terms. To estimate real growth, subtract expected inflation from your return rate, or use our inflation calculator.
What is the Rule of 72?
Divide 72 by your annual return to estimate how many years it takes to double your money. At 8%, money doubles roughly every 9 years.
This content is for general information only and is not investment advice. Consider your own situation and consult a licensed professional before making financial decisions.