Does "I'm on it" mean "I'm doing it" or "I'm going to do it"?

Question

This is a simple question. As the title says, what would it mean in this given context:

A: Can you check this?

B: I'm on it.

In this case, when B says "I'm on it", does he mean he already started the checking and is continuing it, or he will be checking it sooner or later (but not sure when he will be checking it)? What is B trying to convey exactly here? Thanks!

Updated with my research on the web. It seems to me that the phrase could be interpreted either ways. What do your native speakers think?

Answer 1

Yes, it usually implies that the person who says it is either already actively working on a problem or just a few seconds away from beginning to start actively working on a problem. Think logically about it for a second. If something is on the table or on the news, it's not in the process of getting there. It's already there! So, if somebody tells you that they're on it, you can pretty much consider whatever they're doing done. Take a look at this example:

— I need you to make two copies of this document for me real quick.
— I'm already on it! Consider it done!

He has not done it yet, but the idea here is that you can rest assured that he will. It's as though the problem has already been taken care of even though he's actually only beginning to take care of it. Also notice that although the fact that the problem is ALREADY in the process of being taken care of is implied, nothing prevents you from using the adverb already again for emphasis.

Answer 2

According to the Cambridge dictionary, on it means informally doing something that needs to be done, or trying to solve a problem.

In my experience it doesn't imply one or the other. In fact, the joke is that when your boss asks you how something is coming along and you say "Don't worry, I'm on it," it could both be interpreted to mean that you'll start immediately but also that you were already working on it. The joke then comes from the boss interpreting the latter when in reality the situation is the former, essentially giving a false impression without having to directly lie.

In other words, it could mean either interchangeably. If you want to clarify, then you would have to explicitly ask, "Do you mean 'You are doing it already' or 'You are going to do it?'"

Answer 3

I'm on it means that you have already began the task. And, probably, you are doing it now!

Hey, what about the essay?
Well, I'm on it!

This means the other person has already started writing the essay.

However,

this also depends on the task! Say, if the project is very big, you may have started it but currently, you are not doing it! Then too, you use 'on it.'

Hey, what about that big engine project to be submitted?
Yeah, I'm on it...will submit soon.

This does not mean that the person is fixing a screw in his machine at the time of having a conversion. But, overall, he's on the project these days.

Another definition by UrbanDictionary:

A phrase used by an individual in a group suddenly determined to resolve a task or meaningless puzzle (that the others are too lazy to accomplish), usually in attempt to glorify their image or make them feel valuable to that group.