Financing - your opinion? Realistic?

To be fair, you should include the closing fees in the total cost calculation.

That's obviously true...

Have you by any chance calculated the overall effective interest rate of your 120K building savings contract/TA?

You can actually do that quite well with the numbers I mentioned above. If I add a 1200 euro closing fee to the amount, I end up with 21,100 euros that I paid for 120,000 euros. If we neglect the accrued interest because it is only marginal, that results in something between 0.92 and 0.97 percent, depending on how many years it exactly takes until it is paid off.

You can actually quite well with the numbers I mentioned above.

No; you can't do it like that. I mean the overall effective interest rate (which is a "complex" mixture of interest1 and interest2 in a building savings contract/TA construct and the fact that nothing is repaid during the savings phase). This so-called overall effective interest rate is then suitable to compare the whole with a classic annuity loan with the same term.

Ok then maybe that is too high for me. But why shouldn't that be the effective interest rate? After all, that is exactly what I paid over the entire term... it can't be more precise than that. My figures already take into account that nothing is repaid during the accumulation phase... 0.7% of 120,000 over 10 years is 8,400 euros. For the 70,000 loan I then pay another 11,500 euros in interest and 1,200 euros were the fees. If those are all final numbers, then my calculation should work out? My program calculated the 11,500 euros from the sum of the monthly interest payments made or to be made... Well, even if it is not calculated correctly, at least I know what I have to pay in total, although in this case I would be interested in how exactly it should be calculated

Let's be honest, you are a businessman and have never heard of [Zinseszinseffekt] or [Annuitätenformel]? How does that fit together?