Officer + wife want to build a house.

That is not dirt???

Pregnancies can always have huge and costly consequences!

a. instead of 1 child, there are triplets
b. a disabled child could be born who requires comprehensive care
c. the partner cannot re-enter working life after a break
d. in rare cases, mothers suffer serious damage
.
.

These would all be unforeseen financial consequences!
And a blessing of children does not always lead to marriage, and even then it would not financially secure everything through the man's tax benefits, especially not if you plan financially as tightly as Jörg1980, and that is something one can certainly point out!

Yes, there is always a certain risk.

Whether I would accept a deduction of €1300, I cannot confirm. I would always follow the approach that I can more or less cover the deduction + incidental costs myself. So I wouldn’t do more than €1000.

Having triplets or even a disabled child are risks that simply cannot be avoided. That’s life. And if that should be the case, these financial problems can also be solved. I think!!! But Jörg will be able to assess the risk.

600 € for 100,000

Simply calculate for a loan amount of 100,000 € = 600 € monthly payment including 1% repayment. For a bank, the "security/job" certainly plays a role, but the monthly "ability must also fit." With about 3000 € monthly income, the max monthly rate will be around 1200 € - (which also makes sense, because there are other things one wants/should buy.

Topic savings contract for home construction. I have not been able to calculate/seen any affordable and sensible refinancing (and then probably even full financing!?) over a savings contract in the last 4 years. I am happy to face the cost calculation in contrast to a conventional home loan via a "normal bank loan").

There is a saying that goes:
You can save yourself from savings contracts when building, because then it is already too late!!

Thesis on the right timing:
At 20, you are too young
At 30, no time because of children
At 40, in the prime of life
At 50, a house is no longer worth it - because only two remain
At 60, travel -
At 70, "different apartment"

Building a house can be fun and increase the quality of life for yourself and your family ...

I also believe that when you have more money available, you spend more, however, through a marriage (even if, for example, one person stays at home) the income will increase by at most 300 euros! That will never make up for the 1000 euros that are missing. Even if child benefit is now added.

Calculating so drastically that something happens to someone, in whatever way, is probably uncalculable anyway and would also break the neck of someone with a lot of money.

What I still wonder is, why finance house and land together? You can also buy a plot of land now, pay it off on the side, and then build at some point. Where is the disadvantage? Except maybe a building commitment that might exist.

As well as:

If you calculate with a remaining debt of 10 years and then again with the remaining debt for 10 years, then the rate is lower despite taking a 3% higher interest rate. Is that a calculation error or do banks also calculate like that? Because if I calculate consistently over 30 years, my rate is always the same. That is due to the total debt, but isn’t it even less serious if the interest rate rises since the remaining debt has already decreased anyway?

Um, I hope I was able to make myself understood.

Plot + House Construction should be one process

... because otherwise they have no chance of getting a favorable loan from a bank... because they are already "seized" by the 1st bank and the subordinated bank charges up to 0.4% (risk) surcharge, and of course that is taken advantage of.
Construction financing rule of thumb:
at 1% repayment (almost all home builders do this) the loan is paid off after 36 years
at 2% repayment = approx. 26 years
at 3% repayment =

€200,000 at approx. 5% costs at 1% repayment approx. €1000 per month remaining debt €174,000

at 2% repayment that is €1,170 per month - remaining €148,000 = 25 years term
at 3% = €1,336 - remaining €122,000 20 YEARS term

So big goals are great, but my advice is to move in first and save separately. Then you can - but don’t have to...
and as the saying goes, "you can save yourself building savings, because by then it’s already too late... even if the friendly neighbor explains it differently..."