This is a rule that’s pretty much guaranteed to show up on every ACT and SAT, and knowing it can get you an easy couple of points.
It’s = It is
Correct: It’s very rainy outside today, but it might be sunnier tomorrow.
Incorrect: Its very rainy outside today, but it might be sunnier tomorrow.
Its = Possessive form of “It”
Correct: The book has lost its cover.
Incorrect: The book has lost it’s cover.
Its’ = does not exist
It’s vs. its can be tricky because nouns with apostrophes are possessive (e.g., the boy’s hat = the hat that belongs to the boy). As a result, many people very logically mistake it’s ( a pronoun) for the possessive form. Note that on the ACT, its is almost always the correct answer for precisely this reason.
There is, however, a simple trick.
If you see both it’s and its show up as answer choices and aren’t sure which one to choose, plug in it is. If the sentence makes sense, you need the apostrophe; if it doesn’t (much more likely), you don’t need the apostrophe.
Incorrect: Florida, the site of some of the first European settlements in North America, increased it’s population very slowly after being established as a state.
Plug in: Florida, the site of some of the first European settlements in North America, increased it is population very slowly after being established as a state.
Correct: Florida, the site of some of the first European settlements in North America, increased its population very slowly after being established as a state.
Finally, remember that its’ does not exist. (Nor, for that matter, does its’s, which has been known to appear on occasion.) The plural of its is their. Any answer that contains its’ can be automatically eliminated—no exceptions.