Appendixes or Appendices: Which Plural Should You Use?

Appendixes or appendices is a common spelling question because English accepts both forms as plurals of appendix. The best choice depends mainly on context and editorial style. In most academic, technical, and formal documents, appendices is the safer and more familiar option. However, appendixes is also standard English, especially for the anatomical meaning or when a publication prefers a regular English plural.

The singular form is always appendix. It can mean a supplementary section at the end of a book or report. It can also name the small organ attached to the large intestine. Major dictionaries recognize both plural forms, although individual dictionaries and style guides may recommend one form for a particular sense.

Quick Answer

Both appendixes and appendices are correct plurals of appendix. Use appendices for academic papers, reports, books, and formal documents unless your style guide says otherwise. Use appendixes when referring to more than one anatomical appendix or when following a house style that prefers regular English plurals. Above all, choose one form and use it consistently.

TL;DR

• Both plural forms are grammatically correct.
• Appendices is usually preferred in academic and formal writing.
• Appendixes is common for the body part, but it is not limited to anatomy.
• The singular form is always appendix.
• Follow your school, publisher, employer, or style guide when it gives a preference.

Are Appendixes and Appendices Both Correct?

Yes. Merriam-Webster lists appendixes and appendices as accepted plural forms of appendix. Cambridge also recognizes both forms for supplementary sections in books and documents. Therefore, neither spelling is automatically an error.

Still, correctness and preference are not identical. A form can be grammatically valid yet less common in a particular setting. For example, formal reports and academic papers usually favor appendices. By contrast, appendixes follows the ordinary English pattern of adding -es to a word ending in x.

Form	Status	Most Typical Use
appendix	Singular	One document section or one anatomical organ
appendices	Correct plural	Academic, formal, technical, and publishing contexts
appendixes	Correct plural	Anatomy, general English, or a house style that prefers it

The table gives a practical preference, not an absolute rule. Dictionaries allow overlap, so context and consistency matter more than a rigid distinction.

What Does Appendix Mean?

The noun appendix has two main meanings.

First, an appendix can be extra material placed near the end of a book, report, contract, dissertation, or manual. It may contain raw data, questionnaires, maps, legal wording, calculations, interview transcripts, or other supporting details. Cambridge defines this sense as a separate part at the end of a publication that provides additional information.

Second, an appendix can refer to an anatomical structure. In everyday medical discussion, it usually means the vermiform appendix, a narrow pouch attached near the beginning of the large intestine. Merriam-Webster includes both the document sense and the bodily sense under the same noun.

These meanings share a basic idea: something added or attached to a larger whole. Even so, modern usage often favors different plural forms for each meaning.

When to Use Appendices

Use appendices when you are referring to two or more supplementary sections in a formal document. It is the most familiar choice in research papers, dissertations, business reports, technical manuals, government documents, and scholarly books.

For example:

• The dissertation includes three appendices.
• Survey questions appear in the appendices.
• The report’s appendices contain the full data tables.
• Please review Appendices A and B before the meeting.

This preference is visible in professional guidance. Microsoft’s style guide directly instructs writers to use appendices rather than appendixes. UK government guidance also regularly uses appendices for supporting material attached to reports and applications.

Choose appendices when:

• Your university or publisher uses it.
• You are writing under APA or another academic style that commonly favors it.
• Your readers expect formal editorial language.
• The document already labels sections as Appendix A, Appendix B, and so on.
• You want the least surprising choice for an international audience.

Although appendices comes from a Latin plural pattern, it is fully established in modern English. You do not need to italicize it or treat it as foreign.

When to Use Appendixes

Use appendixes when it matches your publication’s house style, when you prefer a regular English plural, or when you are discussing anatomical appendixes. Cambridge specifically gives appendixes as the plural for the body-part sense in its learner’s entry, while allowing both forms for the book-section sense.

Examples include:

• The medical illustration compares two abnormal appendixes.
• The surgeon described the appendixes shown in the case studies.
• The handbook contains two short appendixes.
• Older editions used appendixes instead of appendices.

However, do not assume that appendixes is informal or incorrect. Merriam-Webster accepts it for the noun generally, including the supplementary-material sense. Some respected editorial resources also use the spelling in labels or content categories. Therefore, the form is standard, even though it appears less often in formal academic prose.

The strongest reason to choose appendixes is consistency. If a journal, company, textbook series, or client uses that form, follow the established style unless a governing guide requires something else.

Appendixes or Appendices in Academic Writing

In academic writing, appendices is usually the best choice. Readers commonly encounter headings such as “Appendix A,” “Appendix B,” and “Appendices.” APA-related writing guidance also identifies appendices as the more common form and emphasizes consistency throughout a paper.

A paper with one supplementary section should use the singular:

• Appendix
• Appendix A

A paper with several supplementary sections may use:

• Appendices
• Appendix A: Survey Questions
• Appendix B: Interview Coding Scheme
• Appendix C: Additional Results

Do not label a single section “Appendices.” The heading must agree with the number of sections. Likewise, do not use “Appendix A” unless another appendix exists or your required style uses lettered labeling for a single appendix.

When referring to the material in a sentence, capitalize the word only when it forms part of a specific label:

• The consent form appears in Appendix B.
• Additional consent forms appear in the appendices.
• See Appendices A–C for the complete instruments.

Your institution’s formatting rules override general preference. Therefore, check the thesis manual, assignment instructions, journal guidelines, or publisher’s style sheet before final submission.

Appendixes or Appendices for the Body Part

For the anatomical sense, appendixes is often the clearest choice. It follows the regular English plural pattern and helps some readers distinguish organs from document sections. Cambridge’s main learner’s entry assigns appendixes to the body-part meaning.

However, appendices is not inherently wrong in medical language. Merriam-Webster lists both plurals for the anatomical noun, including in its medical definition. Consequently, a medical publisher may use either form according to its own editorial policy.

Consider these examples:

• The scan showed inflammation in both appendixes.
• The study compared the appendices of several mammal species.
• The textbook illustrates normal and enlarged appendixes.

The first form may sound more natural in general medical English. The second can occur in scientific or anatomical writing. In either case, readers will understand the meaning from context.

Is There a US and UK Difference?

There is no strict rule that assigns one plural to American English and the other to British English. Both forms appear in dictionaries used by US and UK readers. Cambridge’s British and American entries recognize the alternatives, while Merriam-Webster lists both without restricting either one to a single region.

Nevertheless, formal institutions in both countries often choose appendices. Microsoft’s US-facing style guide requires that form, and current UK government guidance uses it in report-writing instructions. Therefore, register and house style usually matter more than geography.

For an article intended for readers in both countries, appendices is generally the safest document-related plural. For anatomy, appendixes can provide a useful distinction, although either form may be accepted.

Why Does Appendix Have Two Plurals?

English borrowed appendix from Latin. Merriam-Webster traces the word through Latin appendic- and appendix, related to a verb meaning “to append” or attach. The plural appendices preserves a Latin-style change from -x to -ces.

Meanwhile, appendixes applies the productive English plural rule. English normally adds -es to nouns ending in x, as in boxes, indexes, and complexes. Because English often keeps both an inherited classical plural and a regularized English plural, the two forms can coexist.

A similar pattern appears in several other nouns:

Singular	Classical Plural	Regular English Plural
index	indices	indexes
matrix	matrices	matrixes
vortex	vortices	vortexes
appendix	appendices	appendixes

The two plurals sometimes develop different preferences by context. For instance, indexes is common for book lists and databases, while indices often appears in mathematics and economics. With appendix, the distinction is less fixed, but appendices dominates formal document usage.

How to Pronounce Appendices and Appendixes

The two plurals have different endings:

• Appendix: uh-PEN-diks
• Appendices: uh-PEN-dih-seez
• Appendixes: uh-PEN-dik-siz

Cambridge provides separate pronunciations for the singular and plural forms. The stress stays on the second syllable.

Writers sometimes misspell appendices because its pronunciation does not preserve the final x sound. Remember that the -ces ending sounds like “seez,” not “kiz.”

Clear Examples in Sentences

The following examples show natural choices in different settings.

Examples With Appendices

• The annual report includes financial appendices.
• Detailed calculations appear in Appendices C and D.
• Her thesis has two appendices containing interview transcripts.
• The policy document places definitions in the appendices.
• Several maps were moved from the main text to the appendices.
• Refer to the appendices for the complete questionnaire.

Examples With Appendixes

• The anatomy atlas shows appendixes in several positions.
• The researchers examined the appendixes of the specimens.
• This edition contains two newly added appendixes.
• The editor retained the spelling appendixes throughout the manual.
• Both appendixes provide useful background information.
• The doctors compared the patients’ appendixes after surgery.

Examples With the Singular Appendix

• The raw data appears in an appendix.
• See Appendix A for the full list.
• The patient had an inflamed appendix.
• Each appendix begins on a new page.

All these sentences can be grammatical. The main goal is to match the form to the context and keep the choice consistent.

Common Mistakes to Avoid

Treating One Form as Always Wrong

The most common mistake is claiming that only appendices or only appendixes is correct. Major dictionaries recognize both. A style guide may prefer one, but a preference is not a universal grammar rule.

Mixing the Forms Without a Reason

Avoid switching between the two spellings in the same document:

• Inconsistent: The report has three appendices. The first two appendixes contain charts.
• Consistent: The report has three appendices. The first two appendices contain charts.

A deliberate distinction between document sections and organs can justify using both. Otherwise, select one form.

Using a Plural for One Section

Use appendix for one item:

• Correct: The appendix contains the survey.
• Incorrect: The appendices contains the survey.

The verb must also agree with the noun:

• The appendix is useful.
• The appendices are useful.
• The appendixes are useful.

Adding an Apostrophe

Neither plural needs an apostrophe:

• Correct: appendices
• Correct: appendixes
• Incorrect: appendix’s, when you mean more than one

Appendix’s is possessive, not plural:

• The appendix’s title was unclear.

A Simple Decision Guide

Use this practical sequence:

1. Check the required style guide or house style.
2. For academic or formal document sections, choose appendices.
3. For anatomy, consider appendixes, especially in general writing.
4. If no rule applies, choose the form your audience expects.
5. Keep the same form throughout the document.

In most uncertain cases, appendices is the safest choice for written materials. Still, appendixes remains correct and may fit anatomy or a regularized editorial style better.

FAQs

Final Takeaway

Both forms are correct, but they do not carry equal preference in every setting. Choose appendices for most academic, professional, and formal document contexts. Choose appendixes when discussing anatomy or following a style that prefers the regular English plural. Most importantly, follow any required guide and remain consistent from beginning to end.