Paying "rent" to the partner... how?

Quite complicated, all the calculations. Therefore, my alternative (/is not suitable for everyone): Be generous in daily life, do the big shopping, treat to vacations, just get involved. And when times are tight, be there and step in. Enjoy pooling together.

Is it his fault that he is building wealth? Is that unfair? De facto, she saves good money by living with him. He even possibly benefits financially from it. Win Win?!

I don’t know what an appropriate answer here should look like. Feels like the squaring of the circle.

Or, yes, there is another option. Don’t move in with him, then financial advantages for each of you are excluded.

A mixing of food costs with housing is not sensible. Just stop that right away.

That leaves what nordanney already said appropriately:

Specifically, if you really want to share everything correctly:
He finances €300k at 1% interest = €250 monthly (since it's an annuity loan, the interest decreases monthly).
Share the amount = your cold rent
Share the additional costs

So €125 plus half of the additional costs, electricity, internet, etc.
The €125 could be slightly increased now, since you "live down" the apartment over time and also sometimes have to pay for repairs. Maybe a total of €350?

Man, , don’t be so grumpy. I don’t know if this is a sensitive topic for you, but I just want an exchange of opinions. I can see that I could save money there, I even wrote that myself...

You can see that there are different perspectives, and those should be discussed. It's not about me refusing to pay even a cent too much. Ideally, it’s our shared life and our home, even if the house isn’t legally mine.

And I am quite willing to pay more than half of the interest, additional costs, and living expenses, because I probably could never afford a house alone, neither to rent nor to buy.

And when it gets concrete, someone else will have a say anyway.

You can also sometimes pay a bill when money is tight or take care of the outdoor plants because it’s a hobbyhorse or buy the new WA.

If you stay together forever, it ultimately doesn’t matter. If you separate, it has to be clean and not leave a bad taste.
If you contributed to building assets, it won’t feel good. If you paid for the vacation, both benefited from it.

How you handle it is up to you. It has to feel right. Now and in the future, no matter how it turns out.

Oh, I'm going to make a science out of this. I can already see it. Sorry, I just enjoy it, I have Excel sheets, household budgets, pension calculations, you wouldn't believe it. (Especially since there's still no money left to buy property yourself.) So please don't get me wrong. For me, it's about cents on paper for fun, I calculate a hundred variants, I look at what makes sense for whom, but it has little to do with real life.

We only have to pay the broadcasting fee once... ooh ooh ooh, saved another 100€. And internet or Prime too... There’s probably liability insurance for shared households as well... That'll make a nice new sheet for my household book. "Savings through living together."