Financing offer single-family house including building savings, experiences

Your installments are already borderline with that salary. I would stop.

Cancellation is not an option for us. :)

But I think we will manage it. I have often read something about 40% of the income, and we are pretty close to that if I don't include the 13th salary and special payments. Of course, this is only a rough guideline and you never know how the job situation will change, but according to my calculations, it should work. And after 10 years, we should have saved quite a bit to simplify the follow-up financing. Here in the forum, I already see many people with very good incomes, so our income seems rather meager in comparison, but our lifestyle should be somewhat more modest from what I can gather. In addition, we won't have children, the commuting costs are practically non-existent, and we are not vacation people. In about 15 years, we can also expect a little support from the parents.

I have often read something about 40% of the income, and we are then quite exact if I do not include the 13th salary and special payments.

Special payments (if regular or guaranteed) and the 13th salary are of course included. They are distributed over 12 months. Then your 40% - although this is just a rule of thumb depending on the absolute income level. At 2k, 40% is way too much. At 20k, it can also be 60% without real problems.

Offer 6
Equity: €39,000
Muscle mortgage: €20,000
Bank total €336,000, 3.24%, theoretically finished after 31 years, installment €1,467
KfW 297 total €100,000, 35 years 2.76% installment €378
Mixed interest rate: 3.20%
Total installment: €1,845

Your offer 6 says on my calculator with 31 years:

The required regular installment is:
€1,423.90
Nominal annual interest rate:
3.193% p.a.
Total interest and fees:
€193,689.45
Total cost:
€529,689.45
Effective annual interest rate:
3.240% p.a.

If I use this installment and subtract your great photovoltaic system:

The required term is:
27.29 years
Nominal annual interest rate:
3.193% p.a.
Total interest and fees:
€155,320.71
Total cost:
€466,320.71
Effective annual interest rate:
3.240% p.a.

Do you really want to spend €63,370 on your photovoltaic system?

Have you considered that it will be broken and need to be replaced anyway during the 31-year term? You will have paid it off for >€60k and it will be broken, haha

Specifically, you would have to divide the costs of the photovoltaic system (63,370€) by the months of the 27.29 years (327 months) duration:

So it is worth it if your electricity bill is reduced by 193€ per month.
Never!!! It pays off.

But go ahead... you have certainly received great profitability calculations from the seller.

Of course, you have to divide by 31 and not by 27!

Then it only comes out to about 170.
That easily works for us. €60 per month feed-in tariff and 4500 kWh per year self-consumption. At 34 cents, that saves €128 per month. Together €188 through the photovoltaic system. So €18 per month left over! It gets even better if electricity prices go up.