Increase repayment or top up building savings?

And since then we have completely caught up the losses and are now in the positive. So where is the problem?

Honestly: If at the time of the extension the depot is in the negative at this level of financing, I simply extend the entire remaining debt, continue to invest in the ETF, and reduce my average purchase price (keyword: cost-average effect), enjoy crazy price jumps in the following months, and then repay the remaining outstanding debt in a lump sum after ten years.

At the same time, I can use the earnings that the MSCI World distributes quarterly to pay the annuity. So where is the problem?

I will take a look at the index over the last few months. My wife had also suggested that maybe ETFs are better. In fact, with our other funds, the cost average effect is gradually becoming positive again. So I need to calculate and think it over. With repayment, I am on the safe side. With ETFs, it is just very variable.

Ultimately, it must be possible for you to have alternatives at time X, in case the stock market is currently in the dumps. If you are confident that you do not necessarily have to make a fire sale in the event of the worst-case scenario, you can take that risk. So if you have something in reserve, can temporarily finance it within the family if necessary, or something similar. And you have to be able to sleep well, even if the stock market is in the dumps or crashes a year before time X. That must not tear you apart mentally (yes, hard to assess, many here only know predominantly rising prices...).

But if it is calculated tightly and you want to play it safe mentally... think about it.

Oh yes, forgot to mention: take a look at longer periods of time as well. Really long. 50 years and more. Otherwise, the very good last ten years might deceive you.