Who publishes this site, and on what data
A financial calculator is only worth what you can verify behind it. Here is where every figure comes from, the method used, and what this site does not claim to do.
The publisher
Cumulo is published by Mohamed ATIA, in a personal capacity, from Belgium. The site, its calculator, its charting engine and the daily price collection are written and maintained by one person.
Let us be clear about what that implies: I am not a licensed financial adviser, not a wealth manager, not a broker. Cumulo is not backed by any financial institution, sells no product, receives no commission from any broker or fund issuer, and never recommends a particular investment.
The site grew out of a simple observation: most savings simulators show a flattering number while quietly skipping the three things that actually determine it — the tax of the country you live in, inflation, and the fact that an average return is never any single year's return. Cumulo shows all three.
A question, a mistake spotted, a correction to suggest: contact@cumulo.be. Error reports are welcome and handled first.
Where the figures come from
No data is typed by hand into the pages. Everything is computed from two sources, each with its own limits.
Thirty years of index series
Annual calendar-year returns, ending 31 December 2025. Every index carries its return type — NR (net dividends reinvested), TR (gross dividends) or PR (price only, dividends excluded) — because comparing a PR index to an NR index understates the former by roughly its dividend yield. The calculation currency is shown too: a euro investor also bore the exchange-rate effect.
The tax regimes of ten countries
Position as at 1 January 2026, for the most common case: a resident individual holding an accumulating equity ETF outside any specific wrapper. Each rule is reproduced with its source of complexity — allowance, exemption, partial relief, annual tax on holdings. The full detail is in the tax comparison.
What the site does not do
An honest tool is judged as much by what it refuses to do.
- No recommendations. No "best ETF", no broker league table, no model portfolio. The funds listed are there because they are widely distributed in Europe, not because they are advised.
- No affiliate links. No link on this site earns anything when clicked. That is what separates a comparison from a sales pitch.
- No forecasts. The calculator's projections are 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.
- No personal data collection. The amounts you enter never leave your browser: they are neither transmitted nor stored. See the privacy policy.
How the site is funded
Cumulo is free, with no account to create and no paid tier. It is funded by display advertising, whose slots are clearly marked as such and placed outside the reading flow.
This deserves to be said plainly, because it is a potential conflict of interest: no advertiser has any say over the content. The tax regimes, returns and fees shown are what they are, including when they are unwelcome. And since the site earns no commission on any financial product, it has no reason to push one over another.
Disclaimer
Cumulo is an educational tool. The figures published are historical data and arithmetic projections: they are neither investment advice, nor a recommendation to buy or sell, nor tax advice.
Past performance does not predict future performance. No guarantee is given as to the accuracy or timeliness of the data shown. Any investment decision is yours alone, and the taxation of your country is set by its administration, not by this site.
The methodology page sets out the formulas used and their limits, calculation by calculation.