What loan amount is realistic for house construction?

That both can think about the project much more together is certainly undisputed. With an income of €3800, monthly expenses of €1700, including €400 for rent (which will then disappear), €2500 remain for the dream house. That doesn't sound unreasonable. But alone... the bank doesn't care whether one of them lives off the strawberries in the garden and makes clothes from their own sheep's wool... no matter how frugal you are, they simply create their household calculation with corresponding amounts and that's it. And with €2350, even as a single person, there are no €1500 left according to this calculation (and the additional costs of the house would still be there). Repayment... I had an offer with 1.6%, that does exist, and it was not from ING.

I am in favor of closing this here. ?

It's just that with the OP, with a possible loan of 430k€ and a desired rate of 1000€, it's barely 1%. But none of that matters when it comes to the numbers. Without involving the girlfriend, there won't be a loan of that amount.

Anyone who can read and calculate knows that it amounts to more than 1000 euros per month. I even specifically wrote the repayment and interest.