Why so confusing?
Using “its” when you really meant “it’s” is a very common punctuation error, and it is easy to understand why it happens. The two forms sound identical.
Not to worry, it is easy to eliminate this error from your writing if you ask yourself one simple question: Do I mean it is or do I mean something belongs to it? If it belongs, do not use an apostrophe — it is not a contraction. “Its” indicates possession.
Rules and Examples
RULE: Use “it’s” when you mean “it is,” and use “its” when you mean “belonging to it.”
Its a trap.
CORRECT: It’s a trap. (Contraction)
Its really long.
CORRECT: It’s really long. (Contraction)
CORRECT: Its really long tail was wagging back and forth. (Possession)
INCORRECT: The tree is losing
CORRECT: The tree is losing its leaves. (Possession)
You can see how each of these easily-confused forms appears in the corpora on Lextutor below. It will give you an idea of the kinds of environments that people use each form most commonly.