Build a new house, is the financial framework possible?

Hello everyone,
my probation period ends tomorrow and I will directly enter a permanent contract, and my girlfriend and I have been "toying" with the idea of buying/building a house for a while now. We have already been to my house bank but have not yet obtained a concrete offer; the advisor's statement was only "we can manage that here," but I am always a bit skeptical about that.

I am 28, my girlfriend/partner is 26.

I just graduated (8 months ago) as a process engineering engineer with currently 52,000 gross or about 2300€ net (37.5h/week).
She is an educator with about 1650€ net (39h/week). Both tax class 1.
Within the next 6 years, I will earn at least 63,540€ (without holiday and Christmas bonuses), depending on tariff increases. She will have about 1750€ net from July/August next year.
Both are permanently employed.

We currently live in an 80m² apartment and pay 800€ warm per month. Our last electricity consumption was 1700 kWh, despite flow heaters in the bathroom and kitchen.
Monthly, each of us pays about 200€ into the account for groceries. Sometimes we spend a bit more, sometimes less.
Fuel costs are around 100€ per month for me due to a long commute, which I partly get back through tax returns. For her, about 20€/month.

Together, monthly expenses for liability and household insurance amount to 23.39€.

My car costs 80€/month (SFK 1/2, so this will decrease in the coming years).
She pays about 30€ per month.
Accident insurance costs me 40€ per month.

As equity, we currently only have what is intended to be put into the house.

[*]21,000€ on my building savings contract which was "financed" by my parents
[*]11,000€ in a daily allowance account
[*]5,000€ in her savings book
[*]5,000€ in her savings book
[*]in total 42,000€

However, as long as nothing concrete happens, we are slowly saving up.

Basically, we initially wanted to buy something finished, but the market here (area postal codes: 41515/41352/41363) currently seems overheated for real estate. That is why we are now much more inclined to build ourselves.
Living space of about 140m² without cellar (gable roof) and 350m² of land is completely sufficient for us.

So far, we have been to Helma, Viebrockhaus, and Okal Haus, but further appointments are still pending. We have almost ruled out Viebrockhaus.
Overall, we want to stay under 400,000€ for land, house, additional building costs, etc. However, we would like KFW40/40+ with air/water heat pump.

For the monthly repayment, we had set 1000€-1100€ excluding ancillary costs with annual one-off payments in the range of 5000€ (Christmas bonus) with an interest rate fixed at about 2.5% for 20 years.

Does that sound realistic and feasible?

Thank you very much for the feedback

Best regards
Eric

Good pay, but the child planning is missing here and why a Kfw40 house if money is tight anyway?

The savings between kfw40 and 55 or Kfw70 are 5 euros per month. Additional costs for construction are probably 20,000-30,000 but I can heat for a long time with that.

How much does a plot of land realistically cost with you? Quickly googling, I find that you have to calculate over 100,000. More like 150,000€? Take a look at the market!

The rest is for the house... minus construction incidental costs, outdoor facilities, etc. I would advise you: save some equity first. A minimum of 2000 per month is possible for you. Your current equity goes towards incidental purchase costs or the kitchen. In this respect, you are at zero. That is a bad basis. Kfw40 or 55 is nice-to-have for those who have these effort costs Über. So start a bit smaller and more average when enough equity has been saved.

In the meantime, you can enjoy your freedom

Hello Eric,
you have already given us part of the necessary information, but some information is still missing. Have you read the pinned post?

It would be great if you would name the construction site.... Not everyone wants to google the postal code. But it is quite close here.

So, I consider it absolutely unrealistic to maintain two cars with 110 euros (80+30). Not even one. Not even a motorcycle. Maybe a scooter.

Whether you can get by with a 1100 euro rate (300,000 EUR loan), I would doubt it here in the region.

125 sqm KfW55 cost us roughly 300,000 EUR without land in Kaarst two years ago.

Not everyone wants to google ZIP codes. But it's right here nearby.

You are neighbors Grevenbroich and something similar

I actually expected something like this, it's even the same district, I just didn't know whether North, South, East, West... and I wasn't in the mood while on the phone.

Honestly... there won't be anything freestanding* under 400-450 THOUSAND EUR here.

*And nothing special.

PS: Actually, this would be something for , she comes from that area. If she doesn't know, then nobody does.