If you’ve ever finished a report, thesis, or ebook and paused before typing the final section heading, you already know the problem. Is it “Appendices” or “Appendixes”? Spellcheck doesn’t flag either one, teachers don’t always agree, and even published books use both. 

This guide settles the confusion for good, explains where each word comes from, and shows you exactly which one to use depending on what you’re writing.

Quick Answer

Both appendices and appendixes are correct plurals of appendix. There is no grammar mistake in choosing either one.

• Appendices — the traditional Latin-based plural, preferred in academic, legal, and formal writing.
• Appendixes — the modern English-based plural, common in everyday, medical, and casual writing.

The real rule isn’t right versus wrong — it’s about context and consistency. Pick one form and use it throughout your document.

Appendices vs Appendixes Meaning

An appendix has two completely separate meanings, and that’s actually where most of the confusion starts.

1. In writing: An appendix is a supplementary section placed at the end of a book, report, or research paper. It holds extra material such as raw data, charts, source documents, or references that support the main text without interrupting its flow.
2. In anatomy: The appendix is a small, finger-shaped pouch attached to the large intestine. It has no major digestive function but can become inflamed, a condition known as appendicitis.

Both meanings share the same singular word, “appendix,” but writers have long debated how each should be pluralized.

Appendices vs Appendixes Difference

The core difference lies in origin, not meaning.

Neither word is “more correct” grammatically. Dictionaries list both as acceptable, and the choice mostly comes down to the audience and the formality of the document.

Also Read This: Vicious vs. Viscous: Learn the Difference With Clear Rules, Examples, Common Mistakes & Correct Usage

Grammar Rule Depth

English plurals generally fall into two camps: words that follow native English rules (adding “-s” or “-es”) and words borrowed from Latin or Greek that keep their original plural pattern.

“Appendix” ends in “-ix,” a Latin suffix. In classical Latin, “-ix” nouns typically pluralize to “-ices,” which is how we get “appendices.” Over time, though, English speakers have increasingly regularized borrowed words, applying the standard “-es” rule instead. That regularization is how “appendixes” became common.

You can see the same pattern play out with other Latin-origin words:

• Index → indices (statistical/mathematical) or indexes (book sections)
• Matrix → matrices or matrixes
• Vortex → vortices or vortexes

In each case, the Latin plural tends to sound more academic, while the English plural feels more casual and accessible.

The Origin of Appendix

The word “appendix” comes from the Latin verb appendere, meaning “to hang upon” or “to attach.” It entered English in the 16th century, originally describing anything attached or added to a larger body of work. The anatomical use came later, once physicians began cataloguing organs by their function (or, in the appendix’s case, apparent lack of one).

Because the word arrived in English through Latin scholarship, its early plural naturally followed Latin conventions. As English evolved into a more self-contained language with its own grammar rules, “appendixes” emerged as a native alternative, especially in everyday and medical contexts.

Why People Confuse Appendices and Appendixes

Several factors keep this debate alive:

• Dictionaries list both without ranking one as more correct, so there’s no single authority to point to.
• Style guides disagree. APA Style favors “appendices,” while some general usage guides accept “appendixes” freely.
• Spellcheck tools don’t flag either spelling, so writers rarely get corrected in real time.
• Regional differences mean British formal writing leans toward “appendices,” while American casual writing often defaults to “appendixes.”
• Mixed exposure. Readers see both forms across books, websites, and papers, reinforcing the idea that either is fine — which it is, just not interchangeably within the same piece.

Which Spelling Should You Use

Think about your audience and setting before choosing.

Use “appendices” when:

• Writing a thesis, dissertation, or academic paper
• Following APA, MLA, or a formal institutional style guide
• Publishing legal, technical, or scientific documents
• Writing for a British or international academic audience

Use “appendixes” when:

• Writing a blog post, casual article, or internal business document
• Referring to the anatomical organ (in medical contexts, “appendixes” is the more standard plural)
• Targeting a general American audience that expects simpler English

If you’re unsure, “appendices” is the safer default for formal writing, since it’s the form most style guides and universities recognize.

Real World Usage of Appendices vs Appendixes

Looking at how professionals actually use these words clears up a lot of the guesswork.

• Academic publishing: Research journals almost always use “appendices” for the supplementary sections at the end of papers.
• Medical writing: Doctors and medical journals commonly use “appendixes” when discussing the anatomical organ in multiple patients, though “appendices” also appears in some clinical literature.
• Business reports: Corporate documents vary, but “appendices” tends to dominate in formal reports, contracts, and compliance documents.
• Everyday content: Blogs, how-to guides, and general web content frequently use “appendixes” because it reads more naturally to a broad audience.

Appendices vs Appendixes in Everyday Examples

Seeing both words in context makes the distinction easier to remember.

• “Please refer to the appendices at the end of this report for the full dataset.”
• “The surgeon removed one of the patient’s appendixes during the operation.” (referring to one of several patients)
• “Our thesis includes three appendices covering survey results, interview transcripts, and raw statistics.”
• “Doctors compared inflamed appendixes across multiple case studies.”
• “The style guide requires all appendices to be labeled alphabetically.”

Common Mistakes with Appendices vs Appendixes

Even experienced writers slip up here. Watch out for these:

1. Mixing both spellings in the same document. Pick one and stay consistent from the first mention to the last.
2. Using “appendices” for the anatomical organ in casual speech. While technically accepted by some dictionaries, “appendixes” sounds more natural in everyday medical conversation.
3. Assuming one form is “wrong.” Both are grammatically valid; the mistake is inconsistency, not choice.
4. Ignoring your style guide. If your university or publisher specifies a form, follow it regardless of personal preference.
5. Overcorrecting with autocorrect suggestions. Some tools default to one spelling and can quietly flip your document’s consistency without you noticing.

Appendices vs Appendixes in Different Contexts

Related Words and Similar Plurals

Appendix isn’t the only English word with this “two correct plurals” situation. Recognizing the pattern helps you handle similar cases with confidence.

• Index: indexes (book sections) vs. indices (mathematics, statistics)
• Cactus: cactuses vs. cacti
• Syllabus: syllabuses vs. syllabi
• Focus: focuses vs. foci
• Formula: formulas vs. formulae

In nearly every case, the Latin-derived plural feels more formal, while the English-regularized plural feels more conversational — the exact same split you see with appendices and appendixes.

Usage Trends

Search and publishing data over the past decade show a gradual shift toward “appendixes” in general web content, driven largely by simplified, SEO-friendly writing that favors plain English. Academic and formal publishing, however, has stayed firmly anchored to “appendices,” since university style guides rarely change once established. In short: casual writing is drifting one way, formal writing is holding steady the other.

Exercise 1: Choose the Correct Form

Select the better option for each sentence based on context.

1. The dissertation included five (appendices / appendixes) with survey data.
2. Both patients’ (appendices / appendixes) were removed during the same week.
3. Please attach your supporting documents in the (appendices / appendixes) section.
4. The blog post added two simple (appendices / appendixes) for extra tips.

(Answers: 1. appendices, 2. appendixes, 3. appendices, 4. appendixes)

Exercise 2: Correct the Sentence

Rewrite each sentence for consistency.

1. “The report has three appendices, but the second appendixes covers financial data.”
2. “Doctors studied several appendices removed from young patients.”

(Corrected: 1. “The report has three appendices, and the second appendix covers financial data.” 2. “Doctors studied several appendixes removed from young patients.”)

Conclusion

The appendices versus appendixes debate isn’t really about right and wrong — it’s about matching your word choice to your writing’s tone and audience. Reach for “appendices” when you’re writing something formal, academic, or research-based, and lean on “appendixes” for casual, everyday, or medical content. Whichever you choose, the golden rule stays the same: stay consistent from the first page to the last, and your writing will always read as polished and professional.

Daniel Brooks

Daniel Brooks  is a passionate writer and digital content creator dedicated to sharing insightful, engaging, and informative articles across multiple niches. With a strong interest in technology, lifestyle, trending topics, and online media, Daniel Brooks focuses on delivering well-researched and reader-friendly content that inspires and informs audiences worldwide.