What's the difference between "its", "it's" and "its'"?

Answer By:  Meenakshi Nandhini, polyglot, once an ESL teacher

I'll tell you a story.

When my son was out watering the plants yesterday, he saw a centaur gallop by. It was a majestic blur against the setting sun.
[it = the centaur]

Today, my neighbour claimed to have found its hoofprints  in her backyard.
[its = possessive form of it; that is, the centaur's hoofprints]

Of course, it's obvious that both of them were mistaken.
[it's = contraction of it is]

But, believe me, it's been really tough to talk them out of their excitement.
[it's = contraction of it has]

Apparently, not everyone knows that centaurs are made-up creatures that do not exist.
[its' = a made-up word that does not exist in English]

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So, it's only its and it's that you need to get sorted out.

Here's a quick and dirty tip:
The apostrophe in it's indicates an elision: Something is missing. That should immediately make you think of it is (with the i missing) or it has (with the hamissing). When you see the apostrophe, expand the elided form in your mind; the meaning will follow.

Consider these three sentences, and try reasoning out how the correct version was derived:

(1)
Yes, ___ my birthday.

Y̶e̶s̶,̶ ̶i̶t̶s̶ ̶m̶y̶ ̶b̶i̶r̶t̶h̶d̶a̶y̶.
Yes, it is my birthday.
 ̶Y̶e̶s̶,̶ ̶i̶t̶ ̶h̶a̶s̶ ̶m̶y̶ ̶b̶i̶r̶t̶h̶d̶a̶y̶.

Correct version: Yes, it's my birthday.

(2)
The dog didn't want to eat ___ food.

The dog didn't want to eat its food.
T̶h̶e̶ ̶d̶o̶g̶ ̶d̶i̶d̶n̶'̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶e̶a̶t̶ ̶i̶t̶ ̶i̶s̶ ̶f̶o̶o̶d̶.
T̶h̶e̶ ̶d̶o̶g̶ ̶d̶i̶d̶n̶'̶t̶ ̶w̶a̶n̶t̶ ̶t̶o̶ ̶e̶a̶t̶ ̶i̶s̶ ̶h̶a̶s̶ ̶f̶o̶o̶d̶.

Correct version: The dog didn't want to eat its food.

(3)
___ been a year since I quit my job.

I̶t̶s̶ ̶b̶e̶e̶n̶ ̶a̶ ̶y̶e̶a̶r̶ ̶s̶i̶n̶c̶e̶ ̶I̶ ̶q̶u̶i̶t̶ ̶m̶y̶ ̶j̶o̶b̶.
I̶t̶ ̶i̶s̶ ̶b̶e̶e̶n̶ ̶a̶ ̶y̶e̶a̶r̶ ̶s̶i̶n̶c̶e̶ ̶I̶ ̶q̶u̶i̶t̶ ̶m̶y̶ ̶j̶o̶b̶.
It has been a year since I quit my job.

Correct version: It's been a year since I quit my job.

I'll leave you with one sentence containing all three forms (it is, it has and its):It's up to every centaur to use the magic it's got to explore its environment without being detected.

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Here's a clear, helpful resource if you need reinforcement:
Its? It's? Or Its'?
Here's another clear explanation. This page also has a little test you can take to evaluate your grasp of this grammar point:
The difference between its and it's (grammar lesson)

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