Is I am finished gramatically correct?

What is the difference between I am finished and I have finished?

Any help would be greatly appreciated.
I think old-time prescriptivists will tell you that "I am finished" will make you sould like a roast ready to come out of the oven.

In real life, no one will bat an eyelash if you say "I'm finished" (or "I'm done").
You seem to be contrasting correct with colloquial. I think this is a false dichotomy. You can have incorrect formal writing as well as correct colloquial expressions.

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I disagree.

Correct usage is "I have finished."

"I am finished" means "I am done for. I am about to die."

And while I have said on several occasions, "I'm done," I have no illusion that this is correct usage--it's just colloquial.
 CalifJim's reply was promoted to an answer.
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