General tools
Compound interest calculator
See how a balance grows with compound interest and regular monthly saving. Everything runs in your browser - nothing is uploaded.
Contributions Interest - compounded monthly, by year
How it works
Compound interest is interest earned on both your original money and the interest it has already earned, so a balance left to grow snowballs over time. This calculator projects that growth. Enter a starting balance, a regular monthly contribution, an annual interest rate, and how many years you will save for, and it returns the final balance, the total you put in, and how much of the end figure is pure interest - plus a year-by-year chart showing your contributions and the interest stacked on top.
Interest here is compounded monthly and your contribution is added at the end of each month, which is how most savings accounts and regular investment plans behave. The longer the time frame, the more dramatic the effect, because later years earn interest on a much larger base - the reason starting early matters so much. The figures are a projection at a fixed rate; real returns vary and inflation eats into them, so treat the result as an illustration rather than a promise. Everything runs in your browser and nothing is sent to a server.
Example. Start with 1,000, add 200 a month at 6% a year for 20 years, and the balance grows to roughly 93,000 - of which about 44,000 is interest on top of the 49,000 you contributed. Stretch it to 30 years and the interest portion overtakes the contributions.
FAQ
How is compound interest calculated?
Each period, interest is added to the balance, and the next period earns interest on that larger balance. This tool applies one twelfth of the annual rate each month and adds your monthly contribution, repeating for the full term - so interest compounds on interest as well as on your deposits.
What is the difference between simple and compound interest?
Simple interest is paid only on the original amount, so it grows in a straight line. Compound interest is paid on the original amount plus all the interest accumulated so far, so it grows faster and faster. This calculator models compound interest.
How often is interest compounded here?
Monthly. Interest is applied twelve times a year and contributions are added at the end of each month. Many real accounts compound monthly or daily; monthly is a close, standard approximation that keeps the year-by-year breakdown easy to read.
Does this account for tax or inflation?
No. It shows nominal growth at the rate you enter, before any tax on the interest and before inflation reduces what the money is worth. For a rough "real" picture, enter a rate closer to your expected return minus inflation.