Minimize Mistakes with This Complete Guide to Hyphens

As a copy editor for nonfiction and history books, I’m struck by how many writers struggle with when to use hyphens and dashes. I get it. This isn’t easy stuff.

I’ve already written about how to use en dashes and about how to use em dashes, the 2-em dash (omission dash), and the 3-em dash.

Today, let’s look at hyphens.

There is a lot to know about this subject. The rules are confusing.

Not only that, but the rules change over time. Yeah. Tell me about it!

Not everyone is up to date with the industry-standard norms laid out in the latest editions of The Chicago Manual of Style (a paid online version is also available and comes with a free trial) and Merriam-Webster’s Collegiate Dictionary.

If you’re frustrated and confused, this post, which is all about hyphens, will help you write and self-edit better. It will help save some time, money, or embarrassment in the future. It will help you better identify what good copyediting entails.

Let’s jump in, shall we?

Hyphens

Hyphens are used to join together compound words or separate syllables within a word. Hyphens are intended to prevent confusion or ambiguity.

When to Use a hyphen

with many compounds, and with parts of speech and specific terms, if the dictionary says so. See “Compounds and hyphenation” below.
with reduplicatives, as in
- rhyming reduplication: hoity-toity; handy-dandy; super-duper
- exact reduplication: bye-bye; boo-boo
- ablaut reduplication (high vowel-low vowel): chit-chat; knick-knack; splish-splash
- shm- reduplication: fancy-schmancy
- with alliteration: lend-lease; flip-flop; tic-tac-toe
- (One exception is flimflam, which is not hyphenated.)
to separate letters when a word is spelled out letter by letter
with a space (or, in a series, by a comma), when the space is a substitute for a word that will be repeated (e.g., fifteen- and thirty-year mortgages; ten-, twenty-, and fifty-dollar bills)
when giving the dimensions of a single entity or a single range, hyphens are used, but there are no spaces or commas: a six-to-ten-year prison sentence
to separate non-inclusive numbers like American telephone numbers, social security numbers, ISBNs, order numbers, and product numbers
in URLs, file names, and email addresses
with dates written in ISO standard date format (YYYY-MM-DD): 2021-01-25
between syllables and to break up a word so that it continues on another line
in some surnames and some first names: Jean-Luc Picard
to join the Arabic definite article, al, to a noun, Al-Qaeda
when informally writing the mass number of a chemical element: C-14 or carbon-14
with musical pitches: G-sharp, or G-♯

Compounds and hyphenation

**For further examples and explanations, see also CMOS, 7.81–89, 5.92–93, and 6.80.

Hyphens are used in compounds when the dictionary says so.

Hyphens are also used to prevent ambiguity or confusion: fast-sailing ship; a man-eating shark; an elaborate re-creation

Compounds that have only recently entered popular usage are more likely to be hyphenated.

Hyphens are used in these compounds:

age + noun: a six-year-old girl
colors + noun: a hunter-green sweater
directions on a compass: north-northwest (but use en dashes when from . . . to . . . is implied: an east–west route)
fraction + noun: a half-mile race; a quarter mile
when writing out fractions: one-half; two-thirds; a two-thirds majority; but not when referring to individual parts divided up or remaining: the final three fourths.
money + noun, spelled out: thirty-three million dollars.
number + noun, including measurements, weights, heights, and time intervals: a four-foot-eleven gymnast; five- or six-minute intervals
ordinal number + noun: twelfth-floor penthouse; twenty-second row
ordinal number + superlative + noun: the fourth-largest city in China (no hyphen: he finished third to last)
large numbers, spelled out (with and without nouns following): seventy-six trombones; twenty-seven
time + noun, in rare instances: the three-thirty flight
gerund + noun: HIV-positive patients
noun + gerund (sometimes): decision-making; bookkeeping
noun + two-function noun: writer-director; player-coach
noun + participle + noun: a rain-soaked day
participle + noun: cutting-edge technology
participle + up, out + and other adverbs + noun: bombed-out buildings; ironed-on patch
adjectival phrases + noun (also known as compound modifiers): an over-the-counter drug (no hyphen: her tone was matter of fact) **See CMOS, 5.92 for more examples and explanations; the goal is to avoid confusing the reader.
noun phrases, if hyphenated in the dictionary: a jack-of-all-trades (no hyphen: a flash in the pan)
verbal phrases, if hyphenated in the dictionary: babysit; sucker punch; strong-arm
proper nouns and adjectives relating to nationality or geography—but only when the first term is a prefix: Franco-Prussian War; Asian American citizens

Consult the dictionary or the hyphenation table in the most recent edition of CMOS for specific words and terms that are hyphenated.

Usually when nouns follow the compound, they are hyphenated, but there are many instances of compounds that are always hyphenated, like cross-reference; dined family-style.

Compounds that are newer in origin and more likely to be misread are more likely to be hyphenated.

Prefixes and hyphenation

Hyphenation rules involving prefixes

Use a hyphen after full or well when it's used in a compound modifier immediately before a noun, unless the word itself is modified: a full-page advertisement; a well-known author (not hyphenated: a very well known author).
Don’t use a hyphen when the modifier is in other positions in the sentence: she works full time; although well known, the author rarely publishes.
The prefixes anti-, co-, post-, pre-, non-, multi-, and re- are rarely hyphenated unless followed by a proper noun: antinuclear; cooperate; postpartum; premature; post-Renaissance; non-Spanish (exception: a word that has recently been invented may be hyphenated).
Use a hyphen when using pro- with a word indicating support (pro-union).
After requires a hyphen when used to form a compound adjective, but not when it's part of a compound noun: after-dinner cocktail; afternoon.
Don’t use a hyphen in a compound noun with vice: vice chairman; vice chancellor.

Examples of compounds formed with prefixes that are hyphenated

before a capitalized word or a numeral: sub-Saharan; pre-1960
before a compound term, such as non-self-supporting entities
to separate repeating vowels, and other combinations that might cause misreading: anti-intellectual; co-opt
- Merriam-Webster’s Collegiate Dictionary closes up nonnegotiable, preempt, and reexamine. M-W hyphenates de-emphasize, but CMOS does not.
to separate the repeated elements in a double prefix: sub-subheading
when a prefix or combining form stands alone: micro- and macroeconomics; over- and underutilized
when the prefix mid- is used with months, years, or centuries: mid-1990s, but not midlife crisis

Don’t hyphenate compounds formed by adverbs ending in “ly”

Compounds formed by 1) adverbs ending in ly + adjective or 2) adverbs ending in ly + participle are not hyphenated. There is no likelihood of ambiguity and the adverb ending in ly indicates that the next word will be another modifier, not a noun: highly complex problem; she is highly regarded

Things you need to remember about hyphens

Over time, words that were once hyphenated tend to get closed up. You may be susceptible to hyphenating words that no longer need to be (or no longer typically are) hyphenated, e.g., co-operate is now cooperate. Similarly, the word email was originally hyphenated.
If you’re not sure, look it up in Merriam-Webster’s Collegiate Dictionary or in the print version of The Chicago Manual of Style or its subscription-based online version,
If you’re still not sure, err on the side of not hyphenating, unless you’re confident that the sentence may be misread.
Since 2017 with the 17th edition, CMOS stipulated that email is no longer hyphenated, and decision-making is now hyphenated whether it appears as an adjective or a noun.
CMOS prefers not hyphenating compound nationalities, regardless of the part of speech: Asian American man.
Change all hyphens between inclusive numbers and months to en dashes.
Use an en dash in place of a hyphen in a compound adjective when one or both of the elements being joined are open compounds or are hyphenated: pre–World War II
The auto-hyphenation feature of word processing and design programs can be turned off for chapter titles and other headings.
Never add hyphens to a word to create line breaks. “The only hyphens that should appear in the manuscript are hyphens that would appear regardless of where they appeared on the page” (CMOS).
Never add a hyphen to a URL to create a line break, and do not let a hyphen that is part of a URL appear at the end of a line.
When “and,” “or,” or “nor” are used as a conjunction in irreversible binomials, hyphens are rarely used: cat and mouse game; bread and butter pickles; slash and burn technique; it was touch and go.
In quoted material, hyphens may be changed to en dashes when an en dash is called for.
A hyphen and the minus symbol are not the same. Don’t use them interchangeably. A minus symbol is used for negative numbers (−34°F) and in mathematical contexts, as in 5−2=3.

*A “zoomed in” look at a minus symbol (left) and a hyphen (right). The minus symbol has a higher vertical position and is longer than the hyphen.*