Current financing offer from the house bank

I can "save" just a minimal amount in the building savings contract to be secured for amount x after the interest expires...

No, it’s not that simple. A building savings contract has two phases: saving phase and loan phase. The transition occurs at the earliest when the contract is ready for allocation. To be ready for allocation, you usually have to save 40% of the building savings amount and additionally reach a certain points score (exact calculation and limit depend on the provider). To repay €200,000 in 20 years, you will need to save about €80,000 during that time. Ignoring interest (almost zero anyway) and the contract fee for now, this comes down to an annual deposit of €4,000 or €333 per month. Taking the contract fee into account, it’s considerably more. This is the minimum deposit; otherwise, there is no loan. Incidentally, this does not guarantee that you will be granted a suitable loan. The allocation still has various pitfalls.

I can minimally "save" with the building savings contract just to be secured for amount x after the interest period expires...

The plan is to build up an ETF portfolio on the side, minimally contribute to the building savings contract for maybe 200k -> interest security and the rest will show with time ;-)

That’s just not really sensible.

On the one hand, low repayment and gambling, and on the other hand burning a lot of money with a building savings contract. It would probably have been cheaper to buy a longer fixed interest rate directly for what it now costs (contract fee, account management fee, and opportunity costs for the deposited amount).

A little bit of self-promotion... I once wrote a blog post on the subject. Google can find it under "Warum ein TA Darlehen keine gute Idee ist".

No, it’s not that simple. A home savings contract has two phases: the savings phase and the loan phase. The transition takes place at the earliest when the allocation maturity is reached. To reach the allocation maturity, you usually have to save 40% of the home savings amount and additionally achieve a certain valuation number (exact calculation and limit depend on the provider).
To repay €200,000 in 20 years, you will therefore have to save a good €80,000 during that time. Ignoring interest (which is almost zero anyway) and the closing fee, you end up with €4,000 deposited per year or €333 per month. Considering the closing fee, a bit more. This is the minimum deposit, otherwise there is no loan.

By the way, this does not guarantee that you will also be allocated a matching loan.

For the sake of completeness, it should be mentioned that he can also split the home savings contract if he saves (too) little to reach the minimum home savings amount... but then he won’t have a €200k loan either and takes on more risk, so basically that’s not its purpose...

The allocation still has various pitfalls

That’s important, yeah. "By the way," trading stocks or similar and then using the possible profit as a lump sum payment into the home savings contract to reach the minimum home savings amount is simply not enough. Valuation number is the key word.

The best years for me are now and not at 60

I hope hauskauf1987 will still see it that way in 20 years, that is in his mid-50s and with a >400K€ heavy follow-up financing.

For the sake of completeness, it must be mentioned that he can also split the building savings contract if he saves (too) little to reach the minimum building savings sum... but then he also doesn’t have a 200k loan and takes on more risk, so basically that’s not its purpose...

That’s important, yep. Trading stocks or similar “on the side” and then using any proceeds as a one-time payment into the building savings contract to reach the minimum building savings sum is not enough. Evaluation number is the keyword.

Thank you You’re absolutely right, I had a faulty line of thought there ;-) I’ll reconsider. The conversation is on Monday. The original plan was minimal savings and then, with high interest, just to take something saved from the building savings deposit to use the low interest rate. But apparently it’s not that simple :D