Which financing option, TH or building savings contract?

Thank you very much for the great info

Gladly. But double-check carefully. The best way is to create an Excel sheet; then you can easily play around with the extra payments.

Is the KFW 124 program actually worthwhile if I do not secure the approximately €31,500 remaining debt after 10 years through a building savings contract?

that is a personal feeling. The house bank will certainly offer a follow-up financing here, as they already have the mortgage. Some also save the remaining debt in parallel

But the "risk" from your main loan is clearly greater than the €31,500 from KfW.

We were at:

So if you make a €3,650 prepayment each year in variant 1 (to better compare it with variant 3), the follow-up interest rate can rise up to 5.9% before variant 3 becomes worthwhile.

You still have some more prepayments planned anyway.

Assuming the interest rate for the KfW revolving credit was 5.9%. Then, with the same installment, it wouldn’t be finished in about 14.5 years but only after 21.9 years.

However, the interest costs increase from €3,500 to €26,000.

Now you could calculate what the costs would be if you put part of the prepayment into a building savings contract instead of into the main loan; there the marginal interest rate is still somewhat higher...

If you notice that interest rates are developing unfavorably, you can always hold back part of your prepayment for the 10-year fixed term.

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Regarding the question of whether the 124 is worthwhile:

Many take it because of the usually lower interest rate compared to the rest of the financing, or the interest-only years. In your case, the money is also cheaper than in the main loan.

I have since received another offer. However, I do not understand how such large differences can arise... with the same loan amount, term, special repayment, adjustment of repayment?!

Via independent financial advisor -> Offer from Ing-Diba:
Loan amount again: €310,000
Nominal/Eff: 1.8/1.85%
Fixed interest period: 15 years
Special repayment: up to 5%
Adjustment of repayment twice free of charge

With BHW I had received 2.26/2.31% for a repayment mortgage (15 years).

When I look at the conditions table at Ing-Diba, these are the conditions for a loan-to-value up to 85% (1.9% minus 0.1% for loans over €300,000). However, we are only paying incidental costs out of our own funds and the remaining equity is not being used but held as a buffer. The advisor asked me if I wanted to perform own services (painting, laying laminate, etc.) and I said yes. But he cannot apply 15% of €310,000, i.e. €46,500, as own work (muscle mortgage), can he? I do not understand how he arrives at 85% loan-to-value or at the interest rate.