I think a more useful question is what fraction of your income do you spend?
Nothing.
I managed to buy a flat during the pandemic, and now my mortgage is ~65% of what I used to pay to rent a single room. And given the situation at the time, I got a very nice interest rate.
It seems to me the spirit of the question is how much one is spending per month to live in their current dwelling. One should include mortgage, taxes, maintenance, and insurance in this calculation.