Compound Capitalization Simulator

Compound Interest Calculator

Discover the power of compound capitalization. Simulate your contributions and observe how accumulated interests accelerate the growth of your wealth.

$5,000
$200
30 years
8%

Total Accumulated Capital

$--
$--
$--
-- x
Your Contributions
Compound Interest
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Annual Projection Table

Year Total Contributed Compound Interest Projected Capital

How the compound interest calculator works

The calculator projects what your investment will be worth if you reinvest the returns and keep contributing every month. Enter the starting amount, the monthly contribution, the expected annual return and the number of years. The chart separates what you paid in from what compound interest generated.

Each month we apply the monthly rate equivalent to your annual return and add the contribution at the end of the month:

Balance(month) = Balance(previous month) × (1 + i) + Contribution, with i = (1 + r)^(1/12) − 1

Worked example

With €10,000 to start, €300 a month and a 7% annual return over 20 years, the result is about €190,958. Of that, €82,000 are your own contributions (€10,000 + €300 × 240 months) and about €108,958 is accumulated growth. From roughly year 13, the interest earned exceeds what you have paid in.

Assumptions and limits

  • Net return. Enter the return after your funds' fees (TER). A 0.5% annual fee kept for 20 years noticeably reduces the final result.
  • Today's money or nominal. If you enter the return before inflation, the result is in nominal euros. To see it in today's purchasing power, subtract expected inflation (for example, 7% − 2% = 5%).
  • Constant return. The calculator uses a fixed average return. Real markets rise and fall, and the order of those years matters, especially once you start withdrawing.
  • Taxes. Capital gains tax is not deducted, as it depends on your country and investment vehicle.

See the formulas and sources in detail in our methodology.

Frequently asked questions

What annual return should I enter?
For a globally diversified equity portfolio, many analyses use 5% to 7% nominal after fees over the long run, or 3% to 5% after inflation. These are historical references, not guarantees: try several scenarios to see the possible range.
Why doesn't the result match other calculators?
Many calculators divide the annual return by 12, which compounds slightly more than the stated annual rate. We use the equivalent monthly rate, so 7% a year returns exactly 7% over twelve months. Whether the contribution is added at the start or the end of the month also matters.
What is the difference between simple and compound interest?
With simple interest only the original capital earns a return. With compound interest, returns are reinvested and earn returns themselves, so growth accelerates over time.
Do you store the figures I enter?
No. The calculator runs in your browser and the figures are not sent to any server.