House construction financing: possible or too tight?

Well, if you don’t question the 200k and consider it really secure, then it’s not a problem.

An inheritance is NEVER certain, at least not the amount, because it could be that "in the last years of life" the house has to be liquidated to cover care costs. There are too many unknowns in the calculation for me! 1. Positive: the existing house is sold better than calculated 2. How are the living expenses plus 400€ made up 3. What kind of house sum is calculated? Turnkey according to the construction service description, so that upgrades are still added? Or already with a considerable buffer 4. Children: how old? Can costs be calculated yet? (school bus, club etc) I like flat rates, but only if I know the background.

Only having 200 € left every month would be a deal breaker for me. It is not uncommon for us to have special expenses. Whether it’s car repairs, birthdays, vacations. Surely not everything is accounted for in the regular expenses.

That almost never works. For example, this week a condensate pump broke down for me.
Then sometimes the lawn mower breaks down, washing machine, school trip, sometimes an "obligation" to go out to eat. All outside of any calculations...
200 € is practically nothing for a home builder.

An inheritance is NEVER certain, at least not the amount, because it can happen that "in the last years of life" the house has to be liquidated to cover care costs.

It was not said that the 200k come from an inheritance. Read correctly.

There are certainly banks that finance this without any problems. The question is always whether it personally seems feasible. For this, I recommend: Keep a household budget and see what you really spend per month or whether you actually set aside money every month, as if you were paying your installment. And see how it feels and whether you manage with it.