See how your savings grow over time with compound interest and regular monthly contributions.
Rates as of Q2 2025 (example)
A compound interest calculator shows how your money can grow over time when the interest you earn is reinvested and starts earning interest of its own. Enter a starting amount, an optional monthly contribution, an expected annual rate of return, and a number of years, and the calculator projects your balance — including a breakdown of how much came from your contributions versus how much came from compound growth.
This calculator compounds interest monthly. Each month, interest is calculated on the current balance (including all prior interest and contributions), then your monthly contribution is added before the next month's interest is calculated.
Formula (with monthly contributions): Balance grows each month as Balance = Balance × (1 + r) + contribution, where r is the annual interest rate ÷ 12. Over many months, this compounding effect means growth accelerates as the balance increases.
Example: Starting with $10,000, contributing $200 per month, at a 7% annual rate of return (example rate — actual returns are not guaranteed and vary with market conditions) over 20 years, the balance grows to roughly $151,000 — of which about $58,000 came from contributions and the rest from compound growth. (Note: all figures in this example are for illustration purposes only and do not represent actual rates or market conditions.)
Compound interest is the basis for how most long-term savings and investment accounts grow, including 401(k)s, IRAs, and regular brokerage accounts. Historical long-term average annual returns for diversified US stock market investments have varied widely over different periods — the 7% figure used as a default in this calculator is a commonly cited illustrative example, not a guaranteed or predicted return. Actual investment returns fluctuate year to year and can be negative, so this calculator is best used for long-term planning rather than predicting a specific outcome.
Compound interest is interest calculated on both your original amount and any interest already earned. Over time, this means your money grows faster than it would with simple interest, which is only calculated on the original amount.
This calculator compounds interest monthly, which is a common assumption for savings and investment accounts. Each month, interest is added to the balance before the next month's interest is calculated.
No. The default rate is an example only, used for illustration. Actual investment returns are not guaranteed, vary year to year, and can be negative. Always use a conservative estimate for your own planning.
A significant amount over long periods. Regular contributions not only add to your balance directly but also start compounding from the moment they're added, so consistent contributions can substantially increase your final balance.
No. This calculator shows nominal growth based on the inputs you provide. Taxes on investment gains and the effect of inflation on purchasing power are not included, and would reduce the real-world value of the projected balance.
This is the effect of compounding — as your balance grows, the interest earned each month also grows, since it's calculated on a larger amount. This is why long time horizons tend to benefit compound growth the most.
Disclaimer: The information, rates, and figures provided on this page are for educational and illustrative purposes only. All rates and examples shown are sample values and do not reflect current or actual market rates or guaranteed investment returns. Financial rules and regulations change frequently. Always consult a qualified financial advisor before making any financial decisions.