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.
Savings target (Sparziel)
A fixed target amount at a given date — what is sought is the monthly instalment that gets you there.
In plain language
Instead of asking “what will my savings instalment become?”, you can turn the question round: “I need 100.000 € in fifteen years — how much do I have to put aside each month?” Two things help enormously: time and a starting sum. Both cut the instalment needed noticeably, because the interest does part of the work. And the other way round: halve the period and you have to save considerably more than twice as much.
In detail
The instalment needed could be computed in closed form from the annuity formula. This calculator deliberately does otherwise: it inverts the verified forward calculation numerically (by bisection) and searches for the smallest instalment whose closing capital reaches the target. The advantage is consistency — there is only one calculation rule, and by construction the result matches the savings plan shown, right down to the rounding to whole cents. Because closing capital grows strictly monotonically with the instalment, the procedure is unambiguous. Costs and taxes on gains are not included; the target is a gross amount.
Worked example
A target of 100.000 € in 15 years at 5 %: with no starting capital it takes 374,13 € a month. With 30.000 € of starting capital the instalment falls to 136,89 € — the starting capital alone grows to 63.411,12 € in that time. With no interest at all, 555,56 € a month would be needed.
In brief
The smallest instalment whose closing capital reaches the target is found numerically.