How to Use a Hyphen

Learn how to properly use hyphens with compound adjectives, and more.

Mignon Fogarty
6-minute read
Episode #347

Using Hyphens with Ages

Several readers’ comments from a previous episode about hyphens had to do with numerals, including ages.

There’s a general rule: if the ages are being used as adjectives or nouns, use hyphens.

  • The five-year-old boy wanted the red balloon. (“Five-year-old” is hyphenated because it’s an adjective that modifies the noun “boy.”)

  • Rudolph is a two-year-old reindeer. (“Two-year-old” is hyphenated because it’s an adjective that modifies the noun “reindeer.”)

You can also use hyphens with implied nouns. For example, since you already know Rudolph is a reindeer, you could say “Rudolph is a two-year-old.” The hyphenated phrase “two-year-old” is essentially modifying the noun you left out: “reindeer.” You can also think of "two-year-old" as a noun--and nouns are usually hyphenated.

However, if the age comes after the noun (or after a noun and a verb, such as "Rudolph is" below), then it doesn’t need a hyphen because it isn't directly modifying the noun.

  • Rudolph is two years old.

  • Our pug is 12 years old.

Words or Numerals with Hyphens?

Many readers had questions about whether you write out numbers or use numerals with hyphens. It’s a style choice, so the best advice is to pick a style guide and stick to it. The Associated Press recommends using words for all numbers less than 10, and the Chicago Manual of Style recommends using words for all numbers less than 100, and their recommendations are no different when you’re using hyphens.

Therefore, if you’re using AP style, you’d write that Santa used a 15-foot sleigh (using the numeral 15), and if you’re using Chicago style, you’d write that Santa used a fifteen-foot sleigh, (writing out the word “fifteen”). Either way, you’d put a hyphen between “fifteen” and “foot” because it’s a compound modifier.

Other Uses for Hyphens

You also use hyphens:

  • with prefixes that come before a word that needs a capital letter, like “anti-American”

  • when separating words with the same three letters in a row, such as “fall-like”

  • when writing numbers twenty-one through ninety-nine, such as

    • thirty-eight* 
    • ninety-nine
    • twenty-five
  • when joining letters and words, like “X-ray” and “A-frame”


About the Author

Mignon Fogarty

Mignon Fogarty is the founder of Quick and Dirty Tips and the author of seven books on language, including the New York Times bestseller "Grammar Girl's Quick and Dirty Tips for Better Writing." She is an inductee in the Podcasting Hall of Fame, and the show is a five-time winner of Best Education Podcast in the Podcast Awards. She has appeared as a guest expert on the Oprah Winfrey Show and the Today Show. Her popular LinkedIn Learning courses help people write better to communicate better.