A compound adjective is a modifier made up of two or more words. The general practice in writing is to use a hyphen if the compound adjective can be misread. There are several exceptions to this rule. The best reference for confirming whether to hyphenate or not hyphenate a word is Webster’s dictionary (11th edition). Here are five rules for using the hyphen.

1
Use a hyphen with comparative and compound adjectives (words ending in er and est).

Examples: longer-term study, best-qualified candidate, highest-rated schools.

2
Use a hyphen in a temporary compound adjective (one that is made up of specially chosen words to best describe something). The hyphen is a crucial tool to give clarity and help readers understand your message. Use it if the word can be misread to change the meaning of your sentence.

Example: The students resided in two parent homes. (This implies two separate residences.)

The students resided in two-parent homes. (This implies that they lived in a home with both of their parents.)

Example: The used-furniture store is popular with students. The hyphen in this case shows that the store sells used furniture.

Whereas “The used furniture store ” implies that the furniture store is used by students.

3
Use hyphens for compound words in which the second word is capitalized.

Example: The program will operate from mid-June to the end of August.

When there is a prefix before a date.

Example: The pre-1945 movie was not included in the curriculum.

With abbreviations:

Example: The pro-MADD parents sponsored after-prom activities for the seniors.

Several related words.

Example: The non-school-based employees work for 12 months of the year.

Words that could easily be misunderstood.

Example: re-form (to form again)

Most words formed with a prefix or suffix are written as one word.

Examples: Prefix: extracurricular, socioeconomic, prekindergarten (BUT pre-K), counterclockwise

Suffix: ladylike; courthouse

4
If a compound adjective is placed after the term it describes, do not use a hyphen, since the combination is clear enough for readers to understand.

Examples: the student-centered activities are new this year, BUT this year, the new activities are student centered.

The program was designed for same-sex children. BUT The program was designed for children of the same sex.

5
When two or more compound adjectives have a common base, the base is often omitted in all but the last adjective, but the hyphens are retained, followed by a space.

Examples: Long- and short-term measures, over- and underfed hamsters, 15- and 30-year mortgages.

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