Land and home financing - together or separately?

Check with your bank whether they would even provide the WI and KfW loans – if that pushes you to a second bank, the interest rate will go up significantly... And think carefully again about whether the QNG KfW component is feasible for you. Have you spoken to an energy consultant about it? How much experience does your preferred construction company have with KfW40 QNG?

I would agree that 3,000 EUR per sqm is not enough – just the extra costs from the energy consultant alone already add up. Plus seemingly everything is "more" and "better". Do you already know the QNG surcharge for the planned house?

Maybe you should prudently plan for only 100,000 EUR first. If it then makes economic sense, and you can get QNG without the savings being less than the costs, that would be a nice bonus...

I don’t understand the entire calculation anyway. Even if I accept your [800,000 EUR financing requirement] (which is not enough, more like 900,000) as interest-free and you want to pay it back in 30 years, I already come to 2,222 EUR/month. Without the 4% for the main loan of 400-500,000 EUR.

Remember. The financial advisor gets paid for closing the deal, not for advising you against such a project.

Have you set WI and KfW to interest-only for 5 years? What do the interest and repayment plans look like for the coming years?

So many components really don't make it easy to keep track. I agree with LotteS that a repayment plan or something similar would probably be helpful. (And definitely check with your bank whether they handle the Kfw stuff, etc.)

How is the installment divided among the loans? (with qng and without) What does your remaining debt look like when refinancing is due? (E.g. after 10, 15, 20 years?) Then maybe also look at what happens if the component to be paid off no longer accrues 0.0x%.

In the end, of course, it's your decision, but I would try out various options and scenarios for that.

We are certainly aware of that. The goal would then be to take out a maximum of another 50-100k from the bank for the house.

Whether she then feels like writing applications for dozens of promotional loans because of a 50k personal loan? The combination is dangerous because the banks usually carry the risk for the promotional loans granted through them. In other words: the bank doesn’t just want a mortgage of 50k entered in the land register, but the entire house financing. And if you either fall out of the funding conditions for one of the loans or they are suddenly discontinued due to lack of money/reorientation/... you have a huge gap.

Many banks are probably glad at the moment if anyone at all still comes and takes out a real estate loan at 4.5%, which was snapped up at 1% two years ago...