End of fixed interest period 2027 - increase repayment or other options?

I would increase the monthly repayment and thus the installment. You then repay evenly, the money is gone and cannot be consumed. In addition, you get used to the higher monthly burden. It’s a classic that I have always warned about. With a historically low interest rate, I set the repayment high and don’t go that low

Or in other words: Why not secure the interest rate for the entire term from the beginning in a historic low interest rate environment?

The only sensible option is the special repayment - which you have not used so far. But this is nothing special, as most people do not do it. So save money annually and put it into the special repayment. You can increase the regular repayment - or the bank says no. Asking does no harm, but it definitely costs money to choose this option. And you first have to recoup the 500e processing fee for it.

So we put everything into the special repayment whenever possible. The money is not eaten up by inflation and it is invested for "us" and not for any banks, funds, etc...

But don't forget to have something in reserve. If, in case of emergency, you have to finance a "new" car at 6% because you don't have the 15,000, in the end, you've also been dealing with lemons ;)

Yes, of course. We'll just see at the end of the year what we can invest.

I want to emphasize once again that this is the safest(!) option, but by far not the only sensible one...

Because you shouldn't calculate the 8% you have to beat with an investment, but the 4% you might pay in 2027 for the follow-up financing, minus the salary increases until then.

On the other hand, real wages are falling, so you are making special repayments with devalued money.