The hyphen ( - ) is a versatile little tool — not to be confused with a dash — that we use to connect two words to create a new compound word, to join prefixes to some words, and to break up words when they can’t fit at the end of a line of text.
A Moving Target
Compound words often evolve from two separate words ("brand new") to a hyphenated word ("brand-new"). Sometimes these evolutions skip the hyphen phase (“blue jeans” is now often written “bluejeans”). New compound words are minted every day — the New York City Subway system recently encouraged riders to pick up a “take-one” at any kiosk; the entertainment industry currently refers to a one-page marketing document as a “one-sheet.”
The best rule is to look it up if you aren’t sure — and be prepared to discover that different dictionaries may tell you different things.
Hyphens can be fun! But if you’re starting to have that not-so-sure-you’ll-be-able-to-figure-it-out feeling, you can find at least some clarity in the following guidelines. Please keep in mind that almost every one of these guidelines has exceptions!
Usually, we hyphenate compound adjectives when they occur before the noun they are describing.
- A medium-rare burger
- A just-in-time field goal
However, we usually don’t use a hyphen when the describing words are after the noun.
- I ordered my burger medium rare.
- The field goal was just in time!
If a compound adjective, made up of an adjective and a noun, expresses a single thought, it is usually hyphenated.
Do NOT use a hyphen when connecting an adverb ending in “-ly” to an adjective to create a compound adjective.
- A really useful tool
- A badly done job
- An overly simplified explanation
- A newly minted coin
Use hyphens for the sake of clarity.
- Man-eating alligator vs. man eating alligator
- Dog-walking company vs. dog walking company
- Free-loader (someone who takes stuff) vs. free loader (a loader that is available to work)
Hyphenate compound words with capital letters.
- A-type personality
Hyphenate numbers between twenty-one and ninety-nine.
- Six hundred and forty-two
Hyphenate physical dimensions and measurements.
- Half-full glass
When you use numbers to form a compound adjective before a noun, include a hyphen, but don’t include one when using numbers as nouns.
- two-hour race vs. the race lasted two hours
- twenty-foot jump vs. she jumped twenty feet
- three-day-old tuna sandwich vs. a tuna sandwich that is three days old
- eight-week-old puppies vs. puppies that are eight weeks old
Use hyphens for ages used as a noun and as an adjective before a noun, but not as an adjective after a noun.
- Twelve-year-olds (noun)
- Twelve-year-old musician (adjective before a noun)
- He is twelve years old. (adjective after a noun)
Use the “suspended hyphen” when assigning forming multiple compound adjectives with numbers.
- The audience consisted of nine- and ten-year-olds.
- The class was assigned 250- and 1000-word essays.