The mix-up of its and it’s certainly deserves recognition as one of the most common errors in written English.

An apostrophe makes all the difference between a possessive pronoun and a contraction. Most words form possession by tacking on an apostrophe and the letter s (‘s) at the end. But that’s not the case with the possessive form of it.

Its is a possessive pronoun and does not have an apostrophe.

A leopard cannot change its spots.

It’s is a contraction for “it is” and always has the apostrophe.

It’s going to partly cloudy with a chance of showers in the afternoon.