When do you use an apostrophe after an s?

An apostrophe is added after an “s” to create the possessive noun form of plural nouns (e.g., “the girls’ shoes”).

An apostrophe is also added after “s” for singular nouns that end in “s” and that have the same singular and plural form (e.g., “ethics’ importance”).

The plural form of other singular nouns that end in “s” is formed by adding an apostrophe and an “s” to the end of the word (e.g., “the princess’s friend”).

Some style guides recommend adding only an apostrophe after certain names ending in “s” (e.g., “Jesus’ followers”). However, adding both an apostrophe and an “s” is recommended by many style guides and reduces inconsistency, so we recommend doing that for all singular names (e.g., “Jesus’s followers,” “Iris’s money”).