Which installment should be paid off first?

Often, only special repayment options amounting to 5% of the loan sum are granted. This means the OP could only repay 2,500 euros with this loan (although it is of course not excluded that 10% were also agreed upon).

With a 5% special repayment option, at least €12,000 remain at the end. Of course, you can also save this on the side and repay it in full at the end of the term. However, a combination of special repayments in tranche 2 and 3 in the first years would also be conceivable. From year 7/8 onwards, you leave out the special repayments on tranche 2 and save it for the final repayment of tranche 3. Depending on interest rate developments, this keeps all options open.

Hello and thank you very much for your suggestions. I think the third part will be covered with a maximum of 2500 euros each year and the rest will be paid off at the end. If there is still some money left during the year, I will invest it as recommended into the loan with the highest interest rate. Let's see how saving and special repayments work out then.

I would make two special repayments on the loan and monitor the interest rate development. If significantly higher interest rates appear after 10 years, make three special repayments on the loan.

If the interest rates remain low, it might be possible to terminate loan 2 early after 9.x years and combine it with loan 3.

Depending on the situation at the end of the fixed interest period, like loan 1.

Always the one with the highest interest rate. You should calculate for yourself once a year for each loan to what extent Sten influences the loan, to get a feeling for it. However, the money is also sometimes quickly spent on something else.