Vanishingly small.

The latest Author Earnings report from Hugh Howey has come out.http://authorearnings.com/the-tenured-vs-debut-author-report/

Interesting stuff.

Here's my takeaway.

Roughly 500 authors debut in the Big 5 publishers per year.

This is a vanishingly small number. 

They also point out that maybe only 300 fiction authors in the Big Five earn a decent living.  Even if they're off by half, that's only 600 authors.  Again, vanishingly small.

The ones on the tippiest top are doing well -- it's a logarithmic scale, though.  It drops off rapidly.

It's not just that you have to be must less than the 1% to be published, but your chances of earning a living even if you do get published are minimal.

I've decided I could take the money I spend on writing and buy lottery tickets and my chances of making money will probably increase....

The odds are better if you self-publish, apparently.  But again, these are the exceptions -- and usually people who are naturals at promoting themselves.

I'm going to keep writing.  Money was never really the object, though I did want to have readers if possible. But even there, I decided that I would write the best books I could and be satisfied with that.

It's a spiritual thing for me.  I figure the universe will figure it out.