Compound interest calculator with side-by-side scenarios

Compounding means that returns earn returns of their own. The longer the period, the larger the effect, which is why time often matters more than the exact amount. Use this simulator to compare scenarios. You can enter any assumed return; the table always shows several side by side so you see the range, not a single number.

Initial amount (€) Monthly contribution (€) Years Assumed annual return (%) Annual inflation (%)

Scenarios side by side

Annual return	Final value	Contributed	Growth	Real value*

* Real value = final value deflated by the inflation you entered, in today's euros.

Illustrative simulation: not a forecast and not a promise of returns. It excludes costs, taxes and the real variability of markets.

How to read the results

These are assumptions, not predictions. Real markets do not grow in a straight line. There are long periods of loss.
Costs reduce the outcome. A small yearly fee compounds against you just as returns compound for you.
Inflation reduces purchasing power. That is why the table shows a real value as well.
Taxes are not included. They depend on your country and the product.

The formula

For a starting amount P, a monthly contribution C, a monthly rate r (annual rate divided by 12) and n months:

FV = P × (1 + r)ⁿ + C × [((1 + r)ⁿ − 1) / r]

A quick mental shortcut is the rule of 72: divide 72 by the annual return in percent to estimate the years needed to double the capital. At 6% that is about 12 years. It is an approximation.

Next, read how ETFs differ from single stocks and what to check before choosing any investment.