Annuity loan - Is a provision interest necessary?

But this can lead to an even bigger following problem:
...

You always have this problem when something costs more than originally planned. :)
So plan well, calculate buffers, and pray a lot. ;)

The problem always arises when something costs more than originally planned. :) So plan well, factor in buffers, and pray a lot. ;)

Exactly, a buffer is included. But what happens now if I don't need this and cannot fully use the agreed loan amount due to lack of further costs and receipts? One would think it's a good case, but not when considering the factor of commitment interest.

You should also talk to your bank about that. Some pay out the money as a lump sum so that you pay the agreed rate. You can do whatever you want with the money or make a special repayment. Option 2 is to reduce the loan accordingly. The problem is that a prepayment penalty could be due on this part.

Exactly, the buffer is included.

I assume that for most it will be rather tight and not leave larger amounts remaining. Otherwise, many things have usually been cut anyway (outdoor facilities) or you put it into the repayment special payment.

For example, we have taken on an additional amount on top of the buffer. After the end of the construction period, we have the option to return up to this amount cost-neutrally.

1. "The non-utilization of loan portions is possible up to an amount of €25,000.00 against a fee of 1% on the non-utilized loan portion."

Am I correct in assuming that if I do not need €10,000, I pay €100 for it, the total loan amount is reduced by €10,000, the conditions remain the same, and I will simply be finished with repaying the entire loan earlier?

2. "During the fixed interest period, the annual repayment rate can be changed twice free of charge between 1% and 10% (in 0.25% increments)."

I don't understand this, can I now, for example (theoretically of course), increase the repayment twice by 2% each time or only twice by 0.25%? Do the 0.25% relate to a monthly increment until the 2% is reached, or how does it work?

To 1: Yes. To 1a: Either the rate remains the same and the term is reduced or To 1b: The rate is reduced and the term remains the same.

Tip: Ask the bank whether it is 1a or 1b. The rule will be 1b, but as a customer I would always want to push for 1a. (Less interest costs)

To 2)

1.00
1.25
1.50
1.75
....
9.75
10.00

Increasing by 2 percentage points twice is not possible if you have already reached 7.00%.

By the way, it should be clearly defined what the repayment rate is calculated from.

2a) Original loan amount 2b) Current loan amount

I would make sure that it is 2a.