How we calculate, and where the data comes from
Every formula and data source the calculator uses, explained without fine print — so you can trust a number before making a decision with your money.
How we calculate
Compound interest
Monthly model: each month the contribution is added (with its possible annual increase) and then the expected return, converted to a monthly rate, is applied. The "real value" also discounts inflation month by month using the same method.
Fees (TER)
The TER is subtracted directly from the expected gross return before simulating: a fund with an 8% return and a 0.20% TER is simulated at a 7.80% net rate, compounded the same as everything else.
Savings taxation (funds, ETFs, crypto)
Gain = final value − contributed capital, taxed with Spain's current savings-tax brackets (19% / 21% / 23% / 27% / 28%), applied progressively to the gain. Transfers between Spanish index mutual funds aren't taxed; selling an ETF or a cryptocurrency to reposition is, every time.
Pension plan taxation
Contributions reduce the general income-tax base (brackets: 19% / 24% / 30% / 37% / 45% / 47%), within the current legal limits (€1,500/year for employees, up to €5,750/year for the self-employed, capped at 30% of net earnings). On withdrawal, the whole pot is taxed as employment income, not as a capital gain — very different taxation from a plain index fund.
Volatility projection (Monte Carlo)
Simulates hundreds of paths with a random monthly return (normal distribution, mean and standard deviation you choose) and shows the 10th/50th/90th percentile of the final balance — an honest way of saying "this is not a guaranteed straight line".
Where the data comes from
Index funds and ETFs
Catalog curated from each manager's official factsheet (TER, tracked index, ISIN, distribution policy). The historical return shown is that of the long-term reference index, not of the specific fund — marked with an asterisk and a disclaimer on every listing. Always check the exact figure on the official factsheet before investing.
Cryptocurrencies
Real-time price from CoinGecko's public API; the rest of the profile (category, consensus, max supply) is approximate.
Historical backtesting (S&P 500, MSCI World, Bitcoin)
Approximate annual returns for 2005-2024 (Bitcoin from 2013), using each year's real sequence instead of a constant average — that way you see the real effect of return order, not just the mean.
Pension plans
A deliberately short catalog: Spanish indexed robo-advisors (MyInvestor, Indexa Capital, Finizens, inbestMe) plus a representative sample of traditional banks, not an exhaustive list. Fee and historical return figures are approximate.
When each catalog was last reviewed
The date is when each catalog last actually changed (additions, removals, or corrected figures), not an external verification we can't prove.
- Fund catalogLast reviewed: 15/07/2026
- Pension plan catalogLast reviewed: 03/07/2026
- Historical data (backtesting)Last reviewed: 08/07/2026
- Asset classes (model portfolios)Last reviewed: 03/07/2026
- Broker/exchange linksLast reviewed: 03/07/2026
Our honesty policy
We'd rather have a shorter, verified catalog than a huge one full of made-up data. When we don't have enough confidence in a specific figure (year-by-year bond or gold return series, for example), we simply don't publish it until we have a verifiable data source connected — we don't fill gaps with unlabeled estimates.
Private area (My account)
Your portfolio data (holdings, contributions, snapshots) is self-reported: we don't connect to your bank or broker. Everything is calculated in your own browser from what you record: wealth evolution carries forward the last known value of each holding; we show both a simple return (current value minus contributed, which ignores when you put in each euro) and an annualized IRR/XIRR that does weight the timing of each contribution — but neither is an audit-grade TWR, since we don't know your portfolio's exact value right before and after each cash flow; your goal progress is projected with a constant return rate you choose, not a prediction; and the MSCI World comparison uses its real annual return, never inventing a figure for years without data yet. The server only stores the values you enter, with access restricted to you alone — not even the site's team can read them (more detail under My account → Data & privacy).
All the content on this site is educational and illustrative, not personalized financial or tax advice. Past returns don't guarantee future returns. Always consult a licensed professional for your specific situation.