The plural of appendix can be confusing because English uses two accepted plural forms: appendices and appendixes. Both forms are recognized in dictionaries, but they are not always equally common in every context. Appendices is especially common when referring to supplementary sections of books, reports, academic papers, and documents, while appendixes is frequently used for the anatomical body part. 

So, if you are asking what is the plural of appendix?, the short answer is appendices or appendixes. The best choice depends on what you mean and, in formal writing, which style guide you are following.

What Is the Plural of Appendix?

The two accepted plural forms are:

Appendix → appendices
Appendix → appendixes

Both are legitimate English plurals. Cambridge lists appendixes for the anatomical sense and appendixes or appendices for the book/document sense. Oxford similarly explains that appendixes is usually used for the body-part meaning, while appendices is usually used for a book or document. 

For most academic, professional, and document-related writing, appendices is an excellent choice.

Quick Answer

Singular	Plural	Common context
appendix	appendices	Books, reports, academic documents
appendix	appendixes	Body parts; also books/documents
appendix	appendaces	❌ Incorrect
appendix	appendix	❌ Singular, not plural

Therefore, if your sentence is:

The report contains three ___.

You can write:

The report contains three appendices.

You can also encounter appendixes, but appendices is particularly common in formal and academic contexts. 

Appendices vs. Appendixes: What Is the Difference?

The difference is primarily usage and context, not a difference in basic grammatical correctness.

Appendices comes from the Latin plural pattern and is widely used for supplementary sections at the end of books, reports, papers, and other documents. Appendixes uses the regular English plural ending and is also accepted. Dictionary.com notes that both forms are valid, while Oxford gives a useful distinction between the body-part and document meanings. 

When to Use Appendices

Appendices is especially natural when discussing:

• Academic papers
• Research reports
• Books
• Legal documents
• Business reports
• Government reports
• Research data
• Supporting tables
• Questionnaires
• Interview transcripts

For example:

The study includes three appendices.

See Appendix B for the complete questionnaire.

APA-style guidance also uses appendices when multiple supplementary sections are included in an academic paper. 

When to Use Appendixes

Appendixes is especially common when referring to multiple anatomical appendixes, although it can also refer to multiple book or document sections.

For example:

The textbook describes several anatomical appendixes.

Cambridge specifically lists appendixes as the plural for the body-part sense. Oxford likewise says the plural is usually appendixes for body parts. 

What Is the Plural Form of Appendix in a Book?

When appendix means a supplementary section at the end of a book, report, article, or document, appendices is a very common plural.

An appendix can contain information that supports the main text without being necessary to include in the main body. Cambridge defines this sense as a separate part at the end of a book or magazine that provides additional information. 

Examples in Books and Documents

• The book contains two appendices.
• The report has four appendices.
• See Appendix A for the survey results.
• Additional data are provided in the appendices.
• The author included three detailed appendices.
• The legal report contains several appendices.
• The research paper includes two appendices.
• The tables are provided in the appendices.
• Supporting documents appear in the appendices.
• The final chapter is followed by several appendices.

For formal writing, appendices is often the safest choice when you mean supplementary sections.

What Is the Plural of Appendix in APA Style?

In APA Style, the plural form is appendices.

When a paper has more than one appendix, APA-style formatting labels them individually, such as:

• Appendix A
• Appendix B
• Appendix C

Scribbr’s explanation of APA 7 confirms that multiple appendices are labeled alphabetically and that appendices is the plural used in APA-style academic writing. 

APA Appendix Examples

You might write:

The full questionnaire is included in Appendix A.

Additional statistical tables are provided in Appendix B.

The interview transcripts are presented in Appendices A and B.

This makes appendices the preferred choice for students and researchers following APA conventions.

What Is the Plural of Appendix in a Document?

For a business, legal, government, or research document, appendices is commonly used when there is more than one supplementary section.

For example:

The contract contains three appendices.

Financial projections are included in the appendices.

The supporting evidence appears in Appendix C.

Cambridge’s Business English Dictionary uses appendices for the plural of an appendix attached to a report or legal document. 

Common Document Examples

• Appendix A: Survey Questions
• Appendix B: Research Data
• Appendix C: Interview Notes
• Appendix D: Technical Specifications

Together, these are the appendices of the document.

What Is the Plural of Appendix in Medical English?

When appendix refers to the organ attached to the large intestine, appendixes is the usual plural in many standard dictionaries.

Oxford specifically states that appendixes is usually used in the body-part sense. Cambridge likewise lists appendixes for the anatomical meaning. 

However, medical dictionaries may recognize both forms. Taber’s Medical Dictionary, for example, lists appendixes and appendices as plural forms. 

Medical Examples

• The surgeon examined the patients’ appendixes.
• The textbook describes abnormalities of the appendix.
• Several rare conditions can affect the appendix.
• The anatomy section discusses the structure of the appendixes.
• Researchers compared the specimens’ appendixes.

For ordinary medical writing, appendixes is a clear and widely recognized choice for the anatomical meaning.

Is Appendices the Plural of Appendix?

Yes.

Appendices is a correct plural of appendix. It is particularly common when appendix refers to additional material at the end of a book, report, paper, or document. Cambridge directly lists appendices as a plural of appendix, and Oxford identifies it as the usual plural in the book/document sense. 

Example:

One appendix → three appendices

Not:

One appendix → three appendaces ❌

Is Appendixes the Plural of Appendix?

Yes.

Appendixes is also a correct plural form. It is not a spelling error.

Cambridge has a separate dictionary entry for appendixes and defines it as the plural of appendix. 

The form is particularly useful for the anatomical meaning:

The patients had inflamed appendixes.

It can also be used for supplementary sections:

The book contains several appendixes.

However, appendices is often preferred in academic and formal document writing.

Why Does Appendix Have Two Plurals?

The word appendix comes from Latin, and appendices preserves the traditional Latin-derived plural pattern.

English also allows the regular plural appendixes, formed by adding -es.

This is not unusual in English. Some words borrowed from Latin or Greek have both a traditional plural and an English plural. In the case of appendix, both forms have become established in English dictionaries. Dictionary.com notes that appendices is the traditional plural and that appendixes is also accepted. 

The Two Patterns

Traditional plural:

appendix → appendices

Regular English plural:

appendix → appendixes

Both are valid, but usage often depends on context.

How Do You Spell Appendix?

The singular word is spelled:

A-P-P-E-N-D-I-X

The plural forms are:

Appendices
A-P-P-E-N-D-I-C-E-S

Appendixes
A-P-P-E-N-D-I-X-E-S

A common mistake is appendaces, but that is not the standard plural.

Spelling Comparison

Form	Correct?
appendix	✅
appendices	✅
appendixes	✅
appendace	❌
appendaces	❌
appendixeses	❌

Plural of Appendix in English | Examples

The correct plural depends on the meaning, but both appendices and appendixes can be found in English.

Examples With Appendices

• The research paper contains two appendices.
• The report includes several appendices.
• See the appendices for supporting evidence.
• The book ends with three appendices.
• The study includes detailed appendices.
• The legal document has four appendices.
• The author added charts to the appendices.
• The data are presented in the appendices.
• Students should read the appendices.
• The final section contains the appendices.

Examples With Appendixes

• The medical text discusses the appendixes.
• The researchers examined the patients’ appendixes.
• The anatomy book describes the appendixes in detail.
• The textbook contains several appendixes.
• The report includes supporting appendixes.
• The researchers compared the anatomical appendixes.
• The book contains four appendixes.
• Additional material appears in the appendixes.
• The authors added technical appendixes.
• The reference guide contains several appendixes.

Plural of Appendix in British vs. American English

There is some variation between dictionaries and contexts, but both appendices and appendixes are recognized in British and American English.

Cambridge’s American Dictionary gives appendices and appendixes for the book/document sense and appendixes for the body-part sense. Oxford similarly distinguishes the usual forms according to meaning. 

Therefore, it is better to focus on meaning and style rather than assuming that one plural belongs exclusively to British English and the other exclusively to American English.

Common Mistakes With the Plural of Appendix

Several incorrect forms appear in searches for this topic, especially appendaces.

The correct forms are appendices and appendixes.

Avoid These Forms

• ❌ appendaces
• ❌ appendixes’s
• ❌ appendixs
• ❌ appendex
• ❌ appendexes
• ❌ appendixeses
• ❌ appendicies
• ❌ appendixies
• ❌ appendix’s as a plural
• ❌ appendix as a plural

The most important distinction is:

One appendix → two appendices / appendixes

Which Is Better: Appendices or Appendixes?

For academic papers, books, research, reports, and formal documents, appendices is generally the better choice because it is especially established in those contexts. APA-style academic writing uses appendices, and Oxford identifies it as the usual plural for the book/document sense. 

For the anatomical organ, appendixes is often the more natural choice.

Simple Rule

Use:

Appendices → books, reports, papers, documents

Appendixes → usually anatomical appendixes

This is a practical guideline rather than an absolute rule, because dictionaries recognize variation.

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10 Quick Facts About the Plural of Appendix

• The singular form is appendix.
• Appendices is a correct plural.
• Appendixes is also a correct plural.
• Appendices is especially common in academic writing.
• APA-style papers use appendices for multiple supplementary sections. 
• Appendixes is commonly used for the anatomical meaning.
• Both forms are recognized by major dictionaries.
• Appendaces is incorrect.
• A single supplementary section is called an appendix.
• Multiple supplementary sections are called appendices or appendixes. 

Conclusion

The plural of appendix has two correct forms: appendices and appendixes. Both are recognized in standard English, but the preferred form often depends on context. For books, research papers, reports, legal documents, and other supplementary material, appendices is especially common. For the anatomical body part, appendixes is usually the more natural form. 

The easiest rule to remember is appendix → appendices for academic and document-related writing, while appendix → appendixes works particularly well for anatomy. Most importantly, avoid appendaces, because it is not a correct plural form.