Number format: this calculator uses German notation throughout — a comma is the decimal separator and a dot groups thousands. “1.234,56” means one thousand two hundred thirty-four euros and fifty-six cents. The figures come from German tax law, so they are shown the way German authorities write them.
Assumed return (Renditeannahme)
The annual growth assumed for an investment — an assumption for the calculation, not a promise about the future.
In plain language
When a calculator says “at 5 % return”, that is an assumption somebody made — not a promise. Broad equity markets have grown roughly in that region over very long periods, but not evenly: there are years with double-digit losses and years with strong gains. So do run two versions, a cautious one and an optimistic one, and see how far apart the results are. That gap is your range of uncertainty.
In detail
The calculation assumes a constant return with monthly compounding. That is a model, not a forecast: real returns fluctuate (volatility), and the order of the years matters as soon as money is withdrawn (sequence-of-returns risk). Not modelled here are product costs (TER), trading costs and spread, nor taxes on gains — Abgeltungsteuer, solidarity surcharge and any church tax, plus the Vorabpauschale on accumulating funds. If you want those included, they are in the compound interest calculator.
Worked example
6 € a day is 182,50 € a month. Paid in over 30 years that is 65.700 € of contributions. At 0 % it stays 65.700 €; at 5 % it becomes 151.887,20 €, at 7 % as much as 222.644,71 €. The spread between the assumptions is larger than the contributions themselves — which is why the assumed return is the most important figure in calculations of this kind.
In brief
Treated as an even annual rate with monthly compounding; real markets fluctuate.