The quick answer

It is astonishingly easy to get some words confused. This is one of the worst offenders.

If you just want the quick version:

• it’s = “it is”
  
• its = something that belongs to it
  

So:

• “it’s two months until my voyage to Mars”
  
• “the dog was very unhappy until I found its chew toy”
  

That is the rule. You can stop here if you like.

Why “its” looks wrong

If you are still here, you are probably wondering why “its” looks like it is missing an apostrophe.

After all, we write:

• Kathy’s bag
  
• my father’s last wishes
  
• the space-port’s tractor beam
  

So why not “it’s toy”?

As an accredited editor working across editing services in Melbourne, I can confirm this is one of the most common sticking points in both general and technical writing.

The answer comes down to nouns and pronouns.

Nouns use apostrophes

Nouns are names of things. Dog. Bicycle. Poland. Wednesday. Fear.

When a noun owns something, it gets an apostrophe:

• the dog’s paw
  
• Poland’s ruler
  
• Wednesday’s timetable
  

Nice and consistent.

Pronouns don’t

Pronouns are words like:

• me
  
• you
  
• he
  
• she
  
• us
  
• them
  
• it
  

They stand in for nouns.

And when pronouns own things, they do not use apostrophes:

• my bike
  
• your wedding
  
• his plans
  
• her sense of humour
  
• our zombie legions
  
• their fault
  
• its eyes
  

No apostrophes anywhere. Not even for “its”.

Why this matters in editing

This is exactly the kind of small but persistent error picked up during proofreading in Melbourne and broader editing services.

It is also a good example of why rules learned at school do not always stick. They are often taught without the underlying logic.

Once you understand that “its” is a pronoun, it stops looking wrong.

The simple rule

Nouns use apostrophes.
Pronouns do not.

(Yes, there is an exception with “one’s”, but that is a whole separate rabbit hole.)

In short

If you are ever unsure, try expanding “it’s” to “it is”.

If that works, you need the apostrophe.
If it does not, you don’t.

And if this is the kind of thing that keeps slipping through, that is exactly what a professional editor in Melbourne is for.