What is the interest rate lock period in construction financing?

I now also have the option with the example 10 fixed interest period.

0.74% interest 2.4 repayment and 12 months provision fee free period.
0.95% 2.4 repayment and 24 months provision fee free period.

1.8% provision fee for both.

Late completion of the semi-detached house according to the purchase contract end of February 2023
But the advisor said that it will probably be a few months earlier.

What would you say?
How can one calculate what is cheaper?

You can calculate with Excel or with various calculators on the internet. At FMH there is a comparison calculator that is quite practical and then tells you which interest rate for the follow-up financing would be advantageous for which loan. You might have to calculate the commitment interest yourself. With the 0.74% you will pay commitment interest throughout the entire construction period, whereby 1.8% on €150,000 is a maximum of €3,000 (a little less since money is being withdrawn). This roughly corresponds exactly to the price difference in the end. But since you also have to pay construction period interest, I would go for the cheaper loan. I would not rely on the seller’s claim that the house might be finished earlier. PS: The calculator is not one hundred percent accurate since you have to finance the commitment interest from equity capital and not from the loan. But I have not found a better way than to enter that as an additional cost.

The KFW also only has a grace period without commitment interest of 12 months and 1.8% interest

If I get an interest rate below 0.95% from the bank, the kfw wohnen loan of €100,000 without repayment subsidy makes no sense since it is more expensive.

I ask myself the following question... If I terminate a 15-year home loan after 8 years (for whatever reasons)... do I have to pay prepayment penalty for the remaining 7 years or only for 2 years (since I could terminate after 10 years)?

2.5 However, you cannot terminate "for whatever reasons".

I was thinking of a house sale.. for whatever reasons.. You mean 2 1/2 years?? Where does the 1/2 year come from?