Using an apostrophe to word ending in "s" can be tricky. Using an apostrophe after the "s" at the end of a word usually occurs when trying to add possession to a noun. Adding another "s" after the apostrophe can look awkward if the word already ends with the letter. Using an apostrophe correctly after a word that ends with "s" is completely dependent upon whether the possession of the noun is singular or plural, or if the "s" is following a number or capital letters.
Add "s" after the apostrophe in a singular possession. For example, if trying to indicate that the actress has a boat, you may write "The actress's boat." This looks awkward, but it is grammatically correct.
Remove the additional "s" when showing plural possession in words ending in "s." Plural possession is when more than one possesses something. For example, "the actresses' dressing room." This indicates that a dressing room belonged to two or more actresses. In plural possession, you don't need to add the additional "s."
Delete apostrophes for numbers and capital letters used as nouns without possession. For example, it is the 1990s, not the 1990's. An example of an inappropriate apostrophe for capital letters is, "She went to the MDs's offices." The correct sentence would be, "She went to the MDs' offices."