Which is correct, “aren’t I?” or “am I not?”
“Aren’t I?” is commonly used and very acceptable in informal language. “Am I not?” is grammatical, but extremely formal, so in most contexts, “aren’t I?” is the preferred choice. The only exception is when you are writing a formal letter or an academic paper, and then you can either use “am I not?,” or even better, restructure the sentence to avoid using either of these forms.
As you know, aren’t is a contraction of are (a form of the verb be) + not. It is used in statements and questions, with you, they, and all other plural subjects, as in the examples below.
Aren’t you going to the movies tonight?
No, we’re having a dinner party, so we aren’t going to the movies.
John and Kelsey are going, aren’t they?
For singular subjects, like he, she, it, Kelsey, and my professor, the correct contraction is isn’t, as in these examples:
It isn't raining anymore.
My professor isn't in her office, so I'll send her an email message.
However, for first person pronoun, I, there is no contraction with the verb be + not. (“Amn’t” is not a word in English.) Therefore, in casual speech and writing, English speakers use aren’t, instead, and except in formal situations, this is considered entirely grammatical.
I hope this helps.
FONTE: http://www.learnersdictionary.com/qa/ar ... r-am-i-not