This Grammar 101 is about YOUR vs. YOU’RE, so let’s get one thing out of the way: UR is never the right answer. At no point in time will you pick an ACT or SAT answer that has “ur” or “Ur” or “UR” in it, and at no point in time will you turn in a paper that has any form or “ur” in it.  Phew, now that that’s off our chest, we can move on. 

I have no statistical evidence to back this up, but if I had to guess what the most common grammatical mistake in the English language is, I would say “your” vs. “you’re.”  There’s a good chance you’re looking at those two words and either thinking, “Yeah, I screw those up all the time,” or “Wait, those are two different words?” If that’s the case, read 4 more sentences and you’ll never mistake the two again.

Your: an adjective pronoun that shows possession.  
For example: Your car is red.  

You’re: a contraction that combines the words “you” and “are”
Example: You’re the smartest student in the world.

The easiest way to figure out which version belongs in a sentence is to do the same thing we did with who’s vs. whose: put “you are” in place of “your” or “you’re” in the sentence and let your ears tell you which one is right. 

For example, let’s say you read this sentence: Your/You’re going to miss the bus. Substitute “you are” into the sentence and see if it sounds good.  You are going to miss the bus. That sentence should sound right to your ears, which means “you’re” is the right word.

However, try this sentence: Your/You’re car is in the driveway. Substitute “you are” into the sentence and see if it sounds good. You are car is in the driveway. That sentence should sound really bad to your ears, which means “your” is the right word.

That’s it! Now you can impress your teachers by never using the wrong one again. Ur welcome.