Compound Interest Calculator
Find out how much your money can grow over time. Enter an initial amount, an optional monthly deposit and an interest rate — the result appears instantly, with a year-by-year breakdown.
| Year | Invested | Interest | Balance |
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How to use
- Enter the initial amount you already have (or 0 to start from scratch).
- Add how much you plan to deposit every month (optional).
- Enter the interest rate and choose whether it is monthly or yearly.
- Choose the time period and press Calculate.
What is compound interest?
Compound interest is interest calculated on both your original money and on the interest it has already earned — in other words, interest on interest. This is what makes long-term investing so powerful: growth accelerates over time, forming the famous "snowball effect".
The basic formula is A = P × (1 + i)ⁿ, where P is the starting amount, i is the interest rate per period and n is the number of periods. When you also make monthly deposits, each deposit starts earning its own compound interest from the moment it enters the account — which is exactly what this calculator simulates, month by month.
Why monthly deposits matter more than the starting amount
A common surprise: someone who starts with nothing but invests consistently every month usually ends up with far more than someone who deposits a lump sum and never adds to it. Time and consistency beat timing. Use the year-by-year table above to see the moment when the interest you earn each year becomes larger than the money you deposit — that is when your money truly starts working for you.
Tips for using this calculator
Compare scenarios: change the rate from 0.5% to 1% per month and watch the difference over 20 years. Test how starting 5 years earlier changes the final balance. Remember that real investments have taxes and inflation, so treat results as estimates for planning, not guarantees.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is always calculated on the original amount only. Compound interest is calculated on the original amount plus all interest already earned, so the balance grows faster over time.
Does the calculator include monthly deposits?
Yes. Each monthly deposit is added at the end of the month and starts earning compound interest from that point on, which is how most savings and investment accounts work.
Should I enter a monthly or yearly interest rate?
Either one — just select the matching option next to the rate field. The calculator converts between them using compound equivalence, not simple division.
Are taxes and inflation included?
No. Results are gross values. Taxes and inflation vary by country and investment type, so use the results as a planning estimate.
Is my data sent anywhere?
No. All calculations happen locally in your browser — nothing you type is uploaded to any server.