The difference between its and it's

The short answer

Its without an apostrophe is a possessive pronoun that shows ownership, similar to his or her. It's with an apostrophe is a contraction that stands for it is or it has. Confusing the two is one of the most common errors in English writing, even among fluent speakers, because both words sound identical when spoken aloud.

• Its = belonging to it
• It's = it is or it has

What each word means

Its functions exactly like my, your, or their: it points to something belonging to a thing rather than a person. For example, the dog wagged its tail, or the company raised its prices. There is no apostrophe because possessive pronouns in English never use one, unlike possessive nouns such as the dog's tail.

It's is always a contraction, formed by joining it with is or has and dropping a letter. It's raining means it is raining. It's been a long day means it has been a long day. Whenever you can expand it's into it is or it has and the sentence still makes sense, the apostrophe belongs there.

How to tell them apart

The simplest test is substitution. Replace the word with it is or it has in your sentence. If the sentence still works, use it's. If it sounds wrong or awkward, use its instead. Try it with these examples: the cat licked its paw becomes the cat licked it is paw, which fails, so its is correct. It's cold outside becomes it is cold outside, which works, so the apostrophe stays.

This test works in reverse, too. If you see it's in a sentence and the substitution creates something odd, like it is book or it has book, then it's is being used incorrectly and its is needed instead. Try the sentence again: the company updated it's website. Substituting gives the company updated it is website, which fails, so the correct form is the company updated its website.

Common mistakes to avoid

Writers often add an apostrophe to its out of habit, since apostrophes usually signal possession, as in Sarah's book. But its already belongs to a small group of possessive pronouns, including his, hers, ours, and theirs, none of which take an apostrophe. Not: the team celebrated it's victory. Correct: the team celebrated its victory.

A related error goes the other way: dropping the apostrophe from it's when a contraction is intended. Not: its been a great year. Correct: it's been a great year, since the sentence means it has been a great year. Reading your sentence aloud and listening for is or has hiding inside the word can catch both kinds of mistakes before you publish.

Remember it

Picture the apostrophe in it's as a tiny stand-in for a missing letter, exactly like the apostrophe in don't or can't. If you cannot mentally expand it's into it is or it has, the word you need is its, with no apostrophe at all.