This seems to be another instance of Italian using simple present to express a near-future event. "I will finish by today" is a likely English idiom paralleling the gist of the Italian.
In English we "cheat" on the future tense by use of present continuous:
"What will you do this afternoon?"
"I am going to the store" or "I will be going to the store" mean the same thing.
In Italian, there sentences like: Arrivano stasera - literally, "they arrive this evening" in idiomatic English would be "They will arrive this evening."
So, it's just idiom.