Annuity loan or interest-only loan in connection with a home savings contract

if building savings contract then without Riester. The building savings contract has the advantage that you can repay much more flexibly and get interest rate security for >30 years. Meanwhile, several banks also offer it if you really need it.

I can agree with that. We had a Wohnriester included in the construction financing, and just the paperwork until you actually get access to the money when you start building is really annoying. It can't have so many advantages that it's worth the hassle.

We had a Wohnriester included in the construction financing, and just the paperwork until you can actually access the money when you start building is really annoying. It can't have so many advantages that it's worth the hassle.

... and afterwards proof of proper use and the prohibition to ever move out of the property again... otherwise reclaiming the received subsidies... or repurchase within two (?) years...

My question regarding this setup would be, what interest rate risk exists or when does it become relevant? I also prefer to calculate with fixed Euronen.

1st option:
no risk, the KFW over equity means payments
Year 1-24 total 593.5k€
Year 25-30 total 51.5k€
KFW redemption 66k€ after 10 years from equity
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makes a total of 711k€ paid, finished after 30 years or with special repayment after 25-26 years

2nd option:
Fixed payments
Year 1-20 annuity loan / installment 1340€ / 321.6k€
Year 1-10 KFW / installment 760€ / 91.2k€
Redemption 1st KFW after 10 years from equity 64k€
makes a total of 476.6k€

Open "risks"
after 10 years 68k€
after 20 years 36k€

Possible refinancing:
- after 10 years: financing the 68k€ with the then freed 760€ (redemption of both KFW loans) at assumed 6.5% interest, term 10 years and full repayment after 20 years, total 91.2k€
- after 20 years the remaining financing of 36k€ remains. With a constant installment of then free 2.1k€, even 15% interest would add another 2 years -> total 50.5k€?
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Would be total costs of 618.5k€ after 22 years in case of absolutely bad interest rate developments

If I have made a gross mistake in the calculation, please clarify me, I am just a "self-calculator with Excel" and hope to be approximately correct with the monthly installments of the partial loans. However, if this is roughly correct, I find the differences quite striking.