Construction of a Single-Family House - Assessment of Our Financial Situation

One more thing about the taxation of the apartment. With a 3% rental yield, you will probably manage, with depreciation and interest on debt, to keep the rent tax-free. There is also a bit of "leeway" regarding the allocation of investments. In the long run, it only makes sense if as little as possible is paid off on the apartment and everything on the house. Additionally, the rent and the value of the apartment (and that tax-free) increase. If everything else fits (location, condition), definitely keep it.

There is an online return calculator for rental apartments from Stiftung Warentest (until 2019 even available as Excel), which calculates the return based on one's own taxable income. Gross/net returns are shown, cost and rent increases as well as rental loss can be taken into account.

Thank you once again for your opinions.

I think, in summary, it can be said that everyone's opinions differ. There are reasons in favor of the apartment, as well as reasons for selling it.
That was actually clear to me from the very beginning. However, there were important objections and comments that one must be aware of.

In detail, I have to discuss the whole matter with my tax advisor and ultimately also with my bank in order to find the most elegant way for us. After all, they know our financial situation and the local market better.

Regards
GradeSchräg

At least they know our financial situation and the local market better.

The tax advisor wants you to keep the apartment. He hopes to prepare the somewhat more extensive tax return for you. The bank, as long as the risk is manageable, wants to sell you as much credit as possible to earn interest. That means both will rather advise you to keep the apartment, even if it might be financially disadvantageous for you.

Here in the forum, you get advice from people who absolutely have no stake in your financial success/failure.

I myself would probably keep the apartment. You don't sell real estate, only in the greatest need – my grandfather always said. Well, that's why I also rent it out ;-) .

Here in the forum you get advice from people who have absolutely nothing to gain from your financial success/failure.

Another point, indeed. Listen to the opinions of the advisors, but remain accordingly critical. As naturally also in forums. And in the end, calculate everything yourself carefully and then decide.