Get rid of high monthly annuity from an old mortgage loan

By the way, the tax "advantage" is 40 euros, not the deductible amount.

Just because of the tax advantage, I wouldn't repay it and because with more equity you get a better interest rate for the single-family house. Stupid question, but why are the 600€ bothering you? Hopefully, that will be mostly covered by the rent.

But this only works if the bank makes a good interest rate offer for the new building and it is therefore worthwhile. And you just have to see about that.

I actually tend in that direction too, if it weren’t for the high monthly burden. For the monthly household burden, it makes a difference whether I pay 600 euros for the next 6 years or 150 euros for the next 25 years (I just made up the last figure, not in the mood to calculate it exactly right now). By the way, the 40 euro tax benefit is monthly. And sure, I also get rent for the apartment, but that is already factored into the household budget.

But now I’ve finally received feedback from the bank: In principle, they would agree to a prepayment penalty with full repayment or an extension of the old loan. BUT: they would also like to finance the new house, please. From the bank’s point of view, that makes sense, I would have said the same in their place. That means for me: if possible, I would keep the old loan because of the tax benefits and stretch it from 6 to 25 years (to lower the annuity). But this only works if the bank makes a good interest offer for the new building and it makes financial sense. And then you just have to see.