Hyphens between Words

Rule 1. Generally, hyphenate two or more words when they come before a noun they modify and act as a single idea. This is called a compound adjective.

Examples:
an off-campus apartment
state-of-the-art design

When a compound adjective follows a noun, a hyphen may or may not be necessary.

Example: The apartment is off campus.

However, some established compound adjectives are always hyphenated. Double-check with a dictionary or online.

Example: The design is state-of-the-art.

Rule 2a. A hyphen is frequently required when forming original compound verbs for vivid writing, humor, or special situations.

Examples:
The slacker video-gamed his way through life.
Queen Victoria throne-sat for six decades.

Rule 2b. When writing out new, original, or unusual compound nouns, writers should hyphenate whenever doing so avoids confusion.

Examples:
I changed my diet and became a no-meater.
No-meater is too confusing without the hyphen.

The slacker was a video gamer.
Video gamer is clear without a hyphen, although some writers might prefer to hyphenate it.

Writers using familiar compound verbs and nouns should consult a dictionary or look online to decide if these verbs and nouns should be hyphenated.

Rule 3. An often overlooked rule for hyphens: The adverb very and adverbs ending in -ly are not hyphenated.

Incorrect: the very-elegant watch

Incorrect: the finely-tuned watch

This rule applies only to adverbs. The following two sentences are correct because the -ly words are adjectives rather than adverbs:

Correct: the friendly-looking dog

Correct: a family-owned cafe

Rule 4. Hyphens are often used to tell the ages of people and things. A handy rule, whether writing about years, months, or any other period of time, is to use hyphens unless the period of time (years, months, weeks, days) is written in plural form:

With hyphens:
We have a two-year-old child.
We have a two-year-old.

No hyphens: The child is two years old. (Because years is plural.)

Exception: The child is one year old. (Or day, week, month, etc.)

Note that when hyphens are involved in expressing ages, two hyphens are required. Many writers forget the second hyphen:

Incorrect: We have a two-year old child.

Without the second hyphen, the sentence is about an "old child."

Rule 5. Never hesitate to add a hyphen if it solves a possible problem. Following are two examples of well-advised hyphens:

Confusing: I have a few more important things to do.

With hyphen: I have a few more-important things to do.

Without the hyphen, it's impossible to tell whether the sentence is about a few things that are more important or a few more things that are all equally important.

Confusing: He returned the stolen vehicle report.

With hyphen: He returned the stolen-vehicle report.

With no hyphen, we could only guess: Was the vehicle report stolen, or was it a report on stolen vehicles?

Rule 6. When using numbers, hyphenate spans or estimates of time, distance, or other quantities. Remember not to use spaces around hyphens.

Examples:
3:15-3:45 p.m.
1999-2016
300-325 people

Rule 7. Hyphenate all compound numbers from twenty-one through ninety-nine.

Examples:
thirty-two children
one thousand two hundred twenty-one dollars

Rule 8. Hyphenate all spelled-out fractions.

Example: more than two-thirds of registered voters

Rule 9. Hyphenate most double last names.

Example: Sir Winthrop Heinz-Eakins will attend.

Rule 10. As important as hyphens are to clear writing, they can become an annoyance if overused. Avoid adding hyphens when the meaning is clear. Many phrases are so familiar (e.g., high school, twentieth century, one hundred percent) that they can go before a noun without risk of confusing the reader.

Examples:
a high school senior
a twentieth century throwback
one hundred percent correct

Rule 11. When in doubt, look it up. Some familiar phrases may require hyphens. For instance, is a book up to date or up-to-date? Don't guess; have a dictionary close by, or look it up online.