50% of a post payout goes to the author and 50% goes to the curators overall. But it's not an exact 50% of your vote comes back to you in rewards, it all depends on when you vote and who votes before and after you. I'm sure there's a mathematical explanation for it somewhere, but when I check my curation payouts, I get less than 30% vote value return when I vote after the whales and I get more than 100% of my vote value if I vote early before any whales.