The large figure is the gross final capital: what your investment would be worth at the chosen horizon, before tax and expressed in that year's euros. It is the number most simulators show on its own. The three that follow are the ones that actually matter.

Paid in and interest break that capital down. The ratio between them is the best measure of the work time has done: over ten years, interest accounts for about a third of the total; over thirty, more than two thirds. The composition chart makes that tipping point visible year by year.

Purchasing power brings the final capital back into today's euros. With 2 % annual inflation, a sum reached thirty years out is worth roughly 45 % less than it looks. That is not an accounting detail: it is the difference between what the number promises and what it will buy.

Net of tax applies the chosen country's regime. Depending on whether you live in Luxembourg, Belgium, France or the Netherlands, the same gross performance leaves a very different result — and the mechanisms are not comparable with one another, as our ten-country comparison sets out.

The projection rests on the compound interest formula — capital × (1 + rate)^years — plus contributions, each compounded over its own remaining time. Six settings then correct that skeleton:

• Country of tax residence. Ten regimes are built in, current as at 1 January 2026, with their wrappers where they exist — PEA, life insurance. Some countries tax the gain on sale, others tax holdings every year: the calculation distinguishes the two.
• The fund's ongoing charges. Taken annually from holdings, they compound in the opposite direction to returns. That is what the "what each point of fees costs" chart quantifies.
• Inflation, which produces the purchasing-power line.
• Volatility, which produces the scenario range.
• Indexation of contributions, to reflect a saving effort that follows your income rather than staying frozen for twenty-five years.
• The actual history of an index, optionally, instead of an average rate: the calculation then replays returns year by year, in the order they occurred.

That last option is the most instructive. It shows that the same average return gives appreciably different outcomes depending on whether the bad years fall early or late — an effect averages hide completely.

Saying so is as useful as the rest.

• Brokerage fees on each purchase, nor transaction taxes, which depend on your broker and your country.
• Changes in legislation. Savings taxation moves often; a twenty-five-year horizon will cross several.
• Your personal situation: tax bracket, allowances, marital regime, other income.
• The risk of having to sell at the wrong moment. It is the most concrete risk and the least modellable. The Crises & cycles page lists the eight drawdown episodes of the last thirty years — their depth, their duration, and how long it took to get back to where you started.

The methodology page details every formula and its limits. The about page sets out where the data comes from and who publishes this site.

Is the calculator free?

Yes, entirely, with no account to create and no paid tier. The site is funded by display advertising and receives no commission on any financial product.

Are my amounts stored anywhere?

No. All calculations run in your browser. The amounts you enter are neither sent to a server, nor stored, nor linked to you.

What rate of return should I choose?

There is no universal right answer. For reference, the MSCI World index returned 8.46 % a year between 1995 and 2025, net dividends reinvested, in dollars — while living through eight negative years out of thirty-one. The profiles offered range from 4 % for a mostly bond allocation to 9 % for equities with a technology bias. You can also load an index's actual history instead of an average rate.

Why does the result change so much by country?

Because Europe uses three very different mechanisms: tax on the gain at sale, an annual tax on wealth, or periodic deemed disposal. A small rate taken every year can cost more than a large rate taken once at the end. The ten-country comparison explains each case.

Is the projection a forecast?

No. It is arithmetic applied to assumptions you choose. A past average return does not repeat identically, and the order in which good and bad years arrive changes the final outcome a great deal.