When to add -’s to a noun for possessive

If the noun does not end in -s, add -’s.

Example sentence: Roy managed to climb out on the driver's side.

Example sentence: Thank you for refunding the children's money.

If the noun is singular and ends in -s or an s sound, add -’s.

Example sentence: Lois's sister spent last year in India.

Example sentence: Her article presents an overview of Marx's teachings.

EXCEPTION:To avoid potentially awkward pronunciation, some writers use only the apostrophe with a singular noun ending in -s: Sophocles’.

Exercises:

The apostrophe 1

The apostrophe 2

Related topic:

Nouns that are not possessive