Asking where are you at is a common grammar mistake, and the mistake and error is as obvious and evident as is the redundancy and repetition of the second part of this sentence and complete thought.
More simply–and less redundant–the word where means at what location, so Where are you at is the equivalent of At what location are you at? Ats a problem–if you ask me! Never use where and at in the same question; just ask where are you instead.
I could go on, but I’d hate to repeat myself.
–Paul
Paul’s book–Literally, the Best Language Book Ever
Everything Language and Grammar 
But properly asked, “Hey, where you at?” that would be correct, right?
Reply from Paul: The entry was about “Where are you at?” and adding a “Hey” in front of it doesn’t make it any different. It’s still redundant–it’s the same as saying “Hey, at what location are you at?”
OK. I purposefully omitted the helping verb with no apparent change in your course. I admit you’re right on the mark, and obviously know where it’s at (Paul cringes again at the sound of fingernails scraping dryly across the blackboard).
I’m surprised you didn’t mention the fact that the sentence also has a dangling preposition. “Where you at” is the worst sentence ever. “Where are you” is no more difficult to say, has no more syllables, and it’s correct.
No, there is a difference.
Where at? is for the location of something stationary (Gde in Russian, Wo in German, etc.)
This as opposed to
Where to? if someone is moving to a location (Kuda in Russian, Wohin in German, etc.)
Where are you at? not the same as, Where are you going?
Therefore, if you want to know where someone is at that moment, Hey, where are you at right now, is perfectly acceptable.
Reply from Paul:
Where to and where at are both abbreviated versions of something else, and it’s up to the user to determine whether those shortcuts are acceptable to him/her; however, that does not change the redundancy of the statement where are you at.
There are many redundant statements in language that are considered acceptable, but that doesn’t make them less of an error of redundancy.
P.S.- Even if there is some grammer rule book that says no “at” at the end of sentences, or whatever, it’s old and outdated.
English is a live language and evolves with the times.
Americans don’t know how to use whom, so it’s pretty much been phased out.
English used to have Thee and You to differentiate respectful you and familiar you (just like in other languages), but it’s been simplified to calling everyone you. Rude, but American.
Another example, ‘google it’. Just recently added to the english language. Not correct, but because everyone uses it, it’s accepted now.
Anything the majority of people use and understand goes and by default becomes correct.
That’s what language is.
Reply from Paul: P.S.: Grammar is spelled with an a, not an e. Oh, wait, that’s not true. It’s a commonly made mistake, meaning it’s widely used; therefore, it must be correct since usage is what determines the correctness of the English language.
I still don’t see what is wrong with “Where you at? I am not saying “Where are you at?”
Reply from Paul: There’s still the repition of where meaning “at what location,” so “where you at” would mean “at what location you at.” Besides, without the “are,” there’s no verb in the question. This is not even to mention that it’s best to avoid ending a sentence with a preposition.
you are at the park today / you were at the park today
the park you are at today / the park you were at today
where you are at is of no relevance to me / where you were at is of no relevance to me
–these seem good–
cf. where you are is of no relevance to me (doesn’t seem the same to me)
–also–
where are you at (temporally)
i.e. where are you at in the book you are reading? / in that book, where are you at?
probably not an ‘at’ in there:
where is it dangerous to go? / **it is dangerous to go at the park / it is dangerous to go to the park
++jiggle the syntax++
Dear Sir,
I’m very greatful for your clarification about WHERE/WHERE AT. I’ve been looking for this to help my students understand.
However, the form “where at” does exist, not for location but for status of action:
Where are you? – I’m still at home.
Where are you at? – I’m still packing up.
Would you care to comment?
Thanks.
I wouldn’t recommend saying “Where are you at?” as a replacement for “How far along are you?” or “What’s your status?”
“Where are you at” in the way that you mentioned is probably more of a colloquial usage, and it’s the same in the sense that “Where are you?” would work just as well.
–Paul
Thanks for replying.
Yes, I agree that “where are you at” for status of action is of colloquial use. But I hear the speakers in the media (TV, radio, newspapers,etc…) use this form rather frequently. Aren’t they supposed to be a reference for the so called “standard american english?”
Thank you.
“Where you at? “, is never grammatically correct even though the English language evolves through time.
“Where are you?” is still the preferred sentence.
I am copy editor for a magazine chain, and a writer. Of course, “where are you” is correct. “Where are you AT”, is redundant, but certainly used a lot, even in television commercials. Since most people seem to find it acceptable, there’s a chance it will become standard English (aaargh!) but, as it makes the speaker sound less intelligent, couldn’t we who are knowledgeable agree to gravitate toward the more correct phrase? Ditch the superfluous word if you want to sound smart.