Hyphen Rules: When to Use a Hyphen (and When Not To)

A hyphen joins words or parts of words so a reader takes them as a single unit: a well-known author, a state-of-the-art laboratory, twenty-two students. It is the shortest of the three dash-like marks, and it is easy to confuse with the en dash and em dash. This guide covers every hyphen rule, the mistakes writers make most, and how the hyphen differs from its longer cousins.

Quick Answer: When to Use a Hyphen

Compound modifiers before a noun.
Hyphenate when the words work together before the noun: a well-known author. Do not hyphenate after the noun: the author is well known.

Written numbers 21 to 99.
Twenty-two, forty-six, ninety-nine, and fractions used as modifiers: a two-thirds majority.

Certain prefixes.
Use a hyphen with self-, ex-, and all-, before proper nouns, to avoid confusion, or when the prefix and root share a letter: self-respect, pre-Victorian, re-cover, anti-inflammatory.

Not after "-ly" adverbs.
No hyphen when an adverb ending in -ly modifies an adjective: a highly rated event, not highly-rated.

What Is a Hyphen?

A hyphen (-) is a short punctuation mark used to join words or parts of words. It is shorter than both the en dash and the em dash. Its primary purpose is to connect compound terms and clarify meaning. The hyphen sits on the keyboard next to the zero on most layouts and requires no special character entry.

Hyphen vs. En Dash vs. Em Dash

These three marks look similar but have distinct uses in professional writing. Knowing which to use prevents the most common dash errors in published work.

Mark	Length	Used for	Example
Hyphen	Shortest	Joins words and parts of words	well-known; self-respect
En dash	Medium	Indicates ranges and connections	pages 45 to 67; 2010 to 2025
Em dash	Longest	Marks strong sentence breaks	Replace with a comma or period for cleaner prose

When to Use a Hyphen

1. Compound Modifiers Before Nouns

When two or more words work together to modify a noun, hyphenate them when they appear before the noun. The hyphen tells the reader that the words function as a single unit of meaning.

Well-known singer
State-of-the-art laboratory
Eight-year-old child
Long-term investment
Peer-reviewed journal

When the same modifiers appear after the noun, hyphens are typically not needed because the words no longer need to be linked to clarify meaning.

The singer is well known.
The laboratory is state of the art.
The child is eight years old.
The investment is long term.

2. Compound Numbers and Fractions

Hyphens are used in written-out numbers from twenty-one to ninety-nine and in fractions when they function as modifiers.

Twenty-two students attended the seminar.
The meeting lasted forty-six minutes.
A two-thirds majority is required to pass the motion.
The bottle is one-quarter full.

3. Prefixes

Most prefixes attach directly to the root word without a hyphen (preexisting, nonprofit, antibiotic). Use a hyphen with a prefix only in these specific situations.

Before proper nouns: pre-Victorian, anti-American, post-Soviet
With self-, ex-, and all-: self-respect, ex-partner, all-inclusive
To avoid confusion: re-cover (to cover again) versus recover (to get better); re-sign (to sign again) versus resign (to quit)
When the prefix ends with the same letter the root word begins with: anti-inflammatory, co-owner, de-emphasize

4. Avoiding Ambiguity

A hyphen can change the meaning of a phrase entirely. Use one when the absence of a hyphen would create confusion.

A small-business owner is the owner of a small business.
A small business owner could be read as a business owner who is short.
Thirty-odd people means slightly more than thirty.
Thirty odd people means thirty people who are strange.

5. Suspended Hyphens

When two compound modifiers share the same second element, you can use a "suspended" or "hanging" hyphen to avoid repetition. The hyphen stays attached to the first part, followed by a space.

The class is for 9- to 13-year-olds.
Both short- and long-term goals were discussed.
The course covers first- and second-year material.

Common Hyphen Mistakes

1. Confusing Hyphens with En Dashes

A hyphen is not the same as an en dash. Use an en dash for ranges, connections, and relationships, not a hyphen. Most word processors will autocorrect a hyphen to an en dash when typed between numbers.

Incorrect: The meeting will run from 1-3 p.m. Correct: from 1 to 3 p.m. (or use an en dash).
Incorrect: See pages 45-67. Correct: pages 45 to 67 (or use an en dash).

2. Hyphenating Adverb-Adjective Combinations

When an adverb ending in "-ly" modifies an adjective, no hyphen is needed. The "-ly" ending already signals that the adverb is modifying what comes next, so the hyphen is redundant.

Incorrect: a highly-rated event. Correct: a highly rated event.
Incorrect: a widely-respected scholar. Correct: a widely respected scholar.

This rule applies only to adverbs ending in "-ly." Adverbs that do not end in "-ly" (well, ill, best, little) still take hyphens in compound modifiers: a well-respected scholar, an ill-conceived plan.

3. Inconsistent Hyphenation

Be consistent with hyphenation across similar constructions within the same document. Inconsistency signals a lack of editorial care to readers and reviewers.

Incorrect: She is a well-respected, high profile expert. Correct: a well-respected, high-profile expert.

4. Unnecessary Hyphens with Prefixes

Most common prefixes do not require hyphens. Modern usage has dropped hyphens from many compound words that historically used them.

Incorrect: pre-existing condition. Correct: preexisting condition.
Incorrect: non-profit organization. Correct: nonprofit organization.
Incorrect: e-mail address. Correct: email address.

When in doubt, check Merriam-Webster. If the dictionary lists the closed form (preexisting, nonprofit, email) as the primary entry, use the closed form.

Quick Reference: Hyphen Rules

Hyphenate compound modifiers before a noun (a well-known author), not after (the author is well known).
Hyphenate written numbers from twenty-one to ninety-nine and fractions used as modifiers.
Do not hyphenate adverb-adjective combinations when the adverb ends in "-ly."
Use an en dash, not a hyphen, for ranges and connections.
Most prefixes do not need hyphens. Use them only with self-/ex-/all-, before proper nouns, to avoid confusion, or when prefix and root share a letter.
When in doubt, consult Chicago Manual of Style, AP Stylebook, or Merriam-Webster.

Frequently Asked Questions

When should you hyphenate compound modifiers?

Hyphenate compound modifiers when they appear before the noun they modify, such as state-of-the-art technology, full-time job, or peer-reviewed journal. Do not hyphenate when the same modifiers appear after the noun: the technology is state of the art, the job is full time, the journal is peer reviewed. The exception is when the compound is listed in the dictionary as permanently hyphenated, in which case the hyphen stays regardless of position.

Do you hyphenate highly rated or widely respected?

No. When an adverb ends in -ly, do not hyphenate it to the adjective that follows, even when the pair appears before a noun. Write a highly rated restaurant or a widely respected scholar, not a highly-rated restaurant. The -ly ending already signals that the adverb is modifying the adjective, so the hyphen would be redundant. This rule applies only to adverbs ending in -ly. Adverbs without that ending, such as well, ill, and best, still take hyphens in compound modifiers: a well-known author, an ill-conceived plan, a best-selling novel.

When do prefixes need hyphens?

Most prefixes do not need hyphens. Use a hyphen with a prefix only in four cases. First, before proper nouns (pre-Victorian, anti-American). Second, with the prefixes self-, ex-, and all- (self-respect, ex-partner, all-inclusive). Third, to avoid confusion with another word (re-cover meaning to cover again versus recover meaning to get better). Fourth, when the prefix ends with the same letter the root word begins with (anti-inflammatory, co-owner, de-emphasize). In all other cases, attach the prefix directly to the root with no hyphen and no space: preexisting, nonprofit, antibiotic, postgraduate.

Can a hyphen change the meaning of a sentence?

Yes. A single hyphen can change a sentence's meaning entirely. Thirty odd people attended suggests approximately thirty strange people, while thirty-odd people attended means slightly more than thirty people. A small business owner could describe a business owner of small physical stature, while a small-business owner clearly means the owner of a small business. This is why editors pay close attention to hyphenation in compound modifiers and treat the hyphen as a clarity tool rather than an optional flourish.

What is the difference between a hyphen, an en dash, and an em dash?

A hyphen is the shortest of the three and joins words or parts of words, as in compound modifiers (well-known) and prefixes (self-respect). An en dash is slightly longer and indicates ranges and connections, as in number ranges (pages 45 to 67) and date ranges (2010 to 2025). An em dash is the longest and marks a strong break in a sentence. Editor World's editorial style favors replacing em dashes with commas, colons, or periods for cleaner, more professional prose.

Is it email or e-mail, nonprofit or non-profit?

Modern usage favors the closed forms: email and nonprofit, without a hyphen. Many compound words that historically used hyphens have dropped them as they became established. The reliable way to decide is to check Merriam-Webster: if the dictionary lists the closed form as the primary entry, use the closed form. This applies to preexisting, nonprofit, email, and many similar words.

Related Punctuation Guides

Hyphens are one of several punctuation areas that trip up writers. For more, see our guides on apostrophe rules and which vs. that.

When to Get Help with Your Writing

Missing or misplaced hyphens are small errors, but reviewers, instructors, and clients notice them, and they change meaning more often than writers expect. A human editor catches the hyphenation issues that automated tools pass over, such as a highly-rated restaurant that should read highly rated, or a small business owner that should read small-business owner.

Editor World provides professional proofreading services, academic editing, and business document editing for clients worldwide. Every editor is a native English speaker from the United States, the United Kingdom, or Canada, and no AI is used at any stage. You choose your own editor from verified profiles, and you can request a free sample edit of your first 300 words before committing to a full edit. A certificate of editing is available as an optional add-on.

Published by Editor World. Founded in 2010 by Patti Fisher, PhD, a graduate of The Ohio State University, Editor World provides professional human-only English editing and proofreading for students, academic researchers, businesses, and authors worldwide. BBB A+ accredited since 2010, with 5.0/5 Google Reviews and 5.0/5 Facebook Reviews. More than 140 million words edited for over 8,000 clients in 65+ countries. Multiple Gold and Bronze Stevie Award winner. Native English editors from the United States, the United Kingdom, and Canada. Less than 5% of applicants are accepted to the editor panel. Recommended by the Boston University Economics Department, University of San Diego, University of Michigan, UCLA, University of Missouri, and more. No AI tools are used at any stage.