Most title-case rules are mechanical. Capitalize the first word. Lowercase the articles. Capitalize the verbs. Once you internalize the basic rules, they fire without conscious thought.

Then you hit a hyphenated compound. Should it be State-of-the-Art or State-Of-The-Art? Is it Mid-Century or Mid-century? And what about temporary compounds like well-known author — how does that behave in a title?

Hyphenated compounds are where every style guide reveals its character. Here's how each one handles them, with practical guidance for writers who don't want to memorize four contradictory rule sets.

The basic question

A hyphenated compound is a word formed by joining two or more parts with hyphens. Mother-in-law. State-of-the-art. Twenty-first-century. Self-aware. Eighty-five. Mid-Atlantic.

Each part of the compound could be a "major" word (a noun, verb, adjective) or a "minor" word (an article, preposition, conjunction). The question for title case is: which parts get capitalized?

There are essentially three approaches across the major style guides:

  1. Capitalize all parts (most styles, with exceptions)
  2. Capitalize only the first part, treat the rest like ordinary words (Wikipedia, sometimes Chicago)
  3. Capitalize each major part, lowercase each minor part (Chicago's full rule)

The Chicago Manual of Style approach

Chicago has the most thought-out and most complex rule. It treats each part of the compound as a separate word in a miniature title, applying the same rules within the hyphens that you'd apply between them.

The Chicago rule, simplified:

  • Capitalize the first element always.
  • Capitalize each subsequent element if it is a major word (noun, pronoun, verb, adjective, adverb).
  • Lowercase each subsequent element if it is an article, preposition, or coordinating conjunction.
  • Capitalize the second element when the first element is a prefix that couldn't stand alone (Anti-, Pre-, Re-, Non-, Mid-, Super-): Anti-Inflammatory, Mid-Atlantic, Super-Sized.
  • Lowercase the second element when it's a particle or short modifier in some specific cases (Stand-up, Get-together).

Practical examples under Chicago:

  • State-of-the-Art Design (of, the are minor and lowercase)
  • Mid-Atlantic Region (Mid- is a prefix; Atlantic is a major word)
  • Self-Aware Robot (Self- is a prefix; Aware is major)
  • Mother-in-Law's Day (in is a preposition, lowercase; Law is major)
  • Twenty-First-Century Problems (each numeric/ordinal element capitalized)
  • Stand-up Comedy (up is a particle attached to stand, lowercase)

The AP approach

AP is simpler: capitalize both parts of a hyphenated compound when both are major words. AP doesn't have the same elaborate distinctions Chicago does about prefixes versus particles.

Practical examples under AP:

  • State-Of-The-Art Design (all parts capitalized in AP, including the Of and The)
  • Mid-Atlantic Region
  • Self-Aware Robot
  • Mother-In-Law's Day
  • Twenty-First-Century Problems

AP's approach treats hyphenated compounds as essentially "force-capitalized" — every word gets the first-letter treatment regardless of part of speech. This is simpler to apply but produces visually heavier titles.

The APA approach

APA (7th edition) follows a rule similar to Chicago for hyphenated compounds, with one specific carve-out: both parts of a hyphenated compound are capitalized, including in the body of a title.

Practical examples under APA:

  • State-Of-The-Art Design
  • Mid-Atlantic Region
  • Self-Aware Cognition
  • Twenty-First-Century Research

The MLA approach

MLA follows a rule essentially identical to Chicago: capitalize each major word in the compound, lowercase each article/preposition/conjunction.

The Wikipedia approach

Wikipedia is the outlier. The Wikipedia Manual of Style explicitly says that the second part of a hyphenated compound is generally not capitalized:

  • Mid-atlantic Region (lowercase second part)
  • Self-aware Robot
  • State-of-the-art Design

This produces visibly lighter titles. If you're contributing to Wikipedia or editing pages there, this is the rule that applies.

The visual comparison

Style State of the art Mid-century
APState-Of-The-ArtMid-Century
ChicagoState-of-the-ArtMid-Century
APAState-Of-The-ArtMid-Century
MLAState-of-the-ArtMid-Century
WikipediaState-of-the-artMid-century

Temporary compounds (created on the fly)

Some hyphenated compounds aren't permanent words — they're created on the spot to modify a noun. Well-known author. Long-lasting battery. Hard-to-find rarity.

These follow the same rules as established compounds in a title. The Well-Known Author (AP/Chicago/MLA). The Hard-to-Find Rarity (Chicago — to is a preposition, stays lowercase). The Hard-To-Find Rarity (AP — all parts capitalized).

Numbers and ordinals

When numbers appear in hyphenated compounds, capitalize each numeric word:

  • Twenty-First-Century Politics
  • Eighty-Five-Year-Old Tradition
  • Twenty-Five-Pound Bag

This is unanimous across all major style guides. Numbers in hyphenated compounds always get the capitalized treatment.

Prefix compounds (Anti-, Pre-, Re-, Non-, Mid-, Super-)

When the first element is a Latin or Greek prefix that wouldn't stand on its own as a word, Chicago and similar styles always capitalize the element that follows:

  • Anti-Inflammatory Treatment
  • Pre-Industrial Society
  • Re-Examining History
  • Non-Compete Clauses
  • Mid-Atlantic States
  • Super-Sized Order

Wikipedia is the exception: it would render these as Anti-inflammatory, Pre-industrial, Mid-atlantic in article titles.

Common errors to avoid

Don't capitalize internal articles and prepositions in Chicago/MLA. State-Of-The-Art is AP style; Chicago style is State-of-the-Art. Be consistent.

Don't lowercase the first letter after a prefix. Even Wikipedia capitalizes the first letter of the title — Mid-atlantic Region starts with a capital M even though the post-hyphen a is lowercase.

Don't add or remove hyphens arbitrarily. The hyphenation pattern in the source text should be preserved. Don't "fix" state-of-the-art to state of the art in a title — that's a separate editorial decision.

Don't apply title-case rules to compound proper nouns. Coca-Cola, Mary-Kate, Daniel-Day Lewis are proper nouns that already have their canonical capitalization. Don't apply rules over them.

What the converter does

Our title case converter applies the correct hyphen rule for the style you've selected. AP capitalizes all parts; Chicago applies the article/preposition rule within hyphens; Wikipedia lowercases the second part. Switching the style pill produces different output for hyphenated compounds immediately, so you can see the difference at a glance.

If you have a lot of hyphenated content to process, the bulk converter handles batches under any style.

A quick rule of thumb

If you don't want to memorize the differences and you just need a reasonable default for most contexts, this works:

  1. Capitalize the first part of every hyphenated compound.
  2. Capitalize the second part if it's a noun, verb, adjective, or adverb.
  3. Lowercase the second part if it's an article (a, an, the), preposition (in, of, on, to), or coordinating conjunction (and, but, or).
  4. For prefix compounds (Anti-, Pre-, Re-, Mid-), capitalize the second part too.

That covers Chicago, MLA, and most of APA without much error. AP fans can capitalize even the articles/prepositions inside hyphens and you'll be right.