Compound Interest Calculator

Enter your starting capital, monthly contribution, expected return and time horizon to see the final value, total contributions and interest earned over time.

About this tool

See How Savings Grow Over Time

Starting capital plus a monthly contribution, compounded over the years, split into what you paid in and what interest added.

Monthly Saving Plans

Enter a starting amount and a monthly contribution, as with an ETF savings plan or a regular deposit.

Interest on Interest

Returns are reinvested, so later years grow faster; the chart shows contributions against compound growth.

Three Clear Numbers

Final balance, total contributed and interest earned at the end of the investment period.

How to use it

  1. Enter the initial deposit and choose the currency.
  2. Add a monthly contribution, or leave it at zero for a one-off investment.
  3. Enter the expected annual return in percent.
  4. Set the investment period in years.
  5. Read the final balance, total contributed and interest earned, and follow the chart year by year.

Frequently asked questions

Is my financial data uploaded to any server?

No. Every calculation, PDF and XML file is produced inside your browser tab with JavaScript and WebAssembly. Nothing is uploaded, stored or logged — the tool also keeps working offline.

Does the calculator account for monthly contributions?

Yes. Recurring contributions are compounded alongside the starting capital, and the chart separates deposits from accumulated interest.

Is the tool really free to use?

Yes. The calculators, the invoice studio and the e-invoice tools are free to use, with no account and no watermark. The free plan has fair-use limits. Optional paid plans add higher limits and features such as customer management, reminders and bookkeeping.

Which return should I enter?

A conservative figure. Savings accounts pay a few percent; broad stock indices have averaged more over long periods but swing a lot from year to year. Taxes, fees and inflation are not deducted, so the real value at the end is lower.

How often is interest added?

Monthly. The annual return is divided by twelve and applied every month, and each monthly contribution is added at the end of the month.