From 0 to 100 in 3 years realistic? | Building obligation

So young and still five years away from the first child, this child will not even be of compulsory school age in ten years.

Unfortunately, we have not yet been able to gain any experience with banks regarding how much credit we could already take out today.

Conversely, the banks have no experience (in the required scale) with you yet. Overall, I see the most sensible approach for you is to aim for an intermediate house. That means you should first tackle the first rung of your property ladder and acquire or build a house for a couple that is not too small even with a child in daycare, but no more than that (i.e., postponing the home theater to the next house).

current warm rent: €900 all-inclusive thanks to a relative’s apartment

We cannot assess that without knowing the size and the market rent.

If the house may cost up to 750,000, we are talking about approximately 200-250 sqm of space. Why does it have to be such a palace right away?

If the house is allowed to cost up to 750,000, we're talking about approximately 200-250 sqm of space.
Why does it have to be such a palace right away?

750,000€ including land + additional costs. My gut feeling tells me that we roughly reach this amount if we build with a basement + smart home + corresponding interior fittings. Maybe I’m also calculating too conservatively and 600,000€ would be enough.

Of course, one could also buy a smaller plot of land, but I find the prices too attractive to want to save on land.

In the overall view, I see aiming for an intermediate house as the most sensible for you. That means first tackle the first rung of your real estate ladder and buy or build a house for a couple, which is still not too small even with a child in daycare, but not more than that (i.e., postponing the home theater to the next house).

Briefly about the current rent: Stuttgart city is 30 minutes away by S-Bahn, 55 sqm with a large terrace and garden. Well-off area.

I can't spontaneously warm up to the idea of building or buying twice. This way, one could save the first house and build 10 years later with significantly more equity. Sure, if the house appreciates in value, I might come out with a good tax-free profit. Or am I seeing this incorrectly?

I would be skeptical as well, from today's perspective, about extrapolating equity over 3 (1.5) years based on a strict savings rate, and your requirements for the house, in my humble opinion, are no small matter either.

But let's assume a loan of 550,000 EUR, that would roughly correspond to a monthly burden of 2,000 EUR. Now we subtract that from the net monthly income, reduce the woman's income by 1,000 EUR due to the child, and also calculate another 500 EUR per month in costs for the child. You can certainly live off the rest, but measured against the planned house standard, that would probably involve one or the other restriction, don’t you think? I’ll leave aside the topic of security and, sensibly, marriage.

Edit: Oh yes, what I actually wanted to say – sorry – the issue with the building obligation is always a tricky one. In our town there are development areas in which even ten years after development not all (sold) plots have been built on, despite only two (!) years being allowed. So it seems that this obligation is not always consistently enforced, and possibly you might pay a (small) penalty and still have more time. This is not to encourage you to do so intentionally, but it is based on my honest observation as well as feedback from acquaintances.

Quite honestly, I don't think the plan is that bad. The strict saving shows you whether you can afford to pay it in the extreme case. I would buy the property as late as possible and finance it with a variable rate. Set the maximum repayment possible here. In the meantime, visit houses, talk to GUs, find and plan the floor plan. There is nothing rationally speaking against it for me.