My girlfriend and I are planning to move in together in ~3 months.

I own a small apartment in Amsterdam, my mortgage, heating, water and electricity is about 2000 Euro a month, and I earn 30% more than she does.

Some context: Amsterdam is damn expensive and in an housing crisis, since living here she's been paying about 1000/m to rent a room. Both of us earn quite well and money isn't tight

What is a fair way to split costs? I've heard everything from she should live here for free because I was paying for everything anyway to we should split everything 50/50, and I'm not sure what is fair.

I don't think 50/50 is fair, because the way I see it, I'm going to get back a fair amount of the money I pay to my mortgage when I sell the apartment.

So what is fair? My gut feeling is something like we split the heating, electricity, groceries etc. 50/50. And she pays say 500 Euro a month for living here (less than half what she's used to paying in rent)