Financing offer - Calculate remaining debt

Purchase of a semi-detached house: €230,000
Modernization costs: €95,000
Furniture: €30,000
Notary fees: €4,600
No property transfer tax, as the sale is within the family.

Equity invested: €106,100

Loan amount: €253,500

Part 1:
Loan amount: €203,500
Nominal interest rate: 1.99% / Effective: 2.02%
Repayment 1.5%
20 years
Installment: €591.85
Remaining debt: €128,210.74
Special repayments up to 5% possible

Part 2:
KFW loan 124
Loan amount: €50,000
Nominal interest rate: 1.25% / Effective: 1.28%
Repayment 3.575% (1 year repayment-free)
10 years
Installment: €201.04 (€52.08 in the repayment-free period)
Remaining debt: €32,982.26

Installment in the first year: €643.93, afterwards €792.89

Note:
In parallel, I continue to pay into a Wohnriester building savings contract that has existed for 2 years.
The balance will be used after 10 years for the full repayment of the KFW loan.
The loan from the building savings contract will not be used.

A special repayment will definitely be possible in the first year.
During the fixed interest period, two free changes of the repayment rate are possible for the loan.
After 10 years, I would then increase the repayment rate, as the KFW loan and the building savings contract will then be finished. (To a minimum rate of €900)


How can I calculate the remaining debt after 20 years if I make a special repayment of €2,500 in the first year and increase the rate to €900 after 10 years?

What do you generally think about the offer?

Too short-sighted... is there any reason not to set the repayment rate for the first component at 2.0 / 2.5 / or even 3.0 %? Every half percent is an additional 85 euros burden per month and saved interest on the other hand. Even in the first 10 years.

First of all, you should always repay the part that causes the highest costs. Of course, I understand the part about the full repayment of the KFW after 10 years. However, your adjustment on the cost side should be the larger and more expensive loan.

How to calculate special repayments and repayment rate changes? With Excel, for example.

The background is that the building savings contract is currently not yet ready for allocation. Of course, I can have the balance paid out and also use it for residential purposes, but then I still lose a €500 closing fee. One can consider over 2% immediately, but more unfortunately does not work with the first module.

2% is now the minimum repayment at many banks, you should definitely consider going above that.

I have calculated it once. With 2% repayment and a repayment rate of €900 after the KFW loan payout (10 years), there is an outstanding debt of around €79,000 after 20 years.

That sounds reasonable to me for now. What do you think? This amount would then not be secured in the event of an interest rate increase.

Although with 2% repayment, there might also be a better interest rate from the bank. This is not included now.

Would be fine for me. Especially considering the depreciation of money over 20 years.