Translation:From today on, I am the boss here!
Why wouldn't, "After today, I'm the boss here," be correct?
"Vanaf" doesn't mean after: "vanaf vandaag" includes today.
Why not, from here on I'm the boss?
I believe they like to keep things as literal as possible and still retain the same sense, so since the Dutch sentence includes "vandaag," we should include "today" in the English translation.