Appendices or Appendixes: What's the difference & usage? 2026

English learners and even native speakers often get confused when it comes to plural forms of words, and “appendix” is a prime example. Many wonder whether the plural should be “appendices” or “appendixes”, and the answer can depend on where you are UK or US English. This confusion is common in academic writing, medical texts, and professional documents, where the proper plural is important for clarity and correctness.

Understanding the difference between appendices and appendixes is essential for writers, students, and professionals alike. Not only does it help you avoid embarrassing mistakes, but it also ensures your writing is taken seriously in both British and American contexts. Moreover, knowing the correct form enhances your credibility in formal communication, especially in research papers, reports, and technical documents.

Whether you are writing a medical report discussing the human appendix or compiling supplementary material for a book or research paper, using the correct plural is crucial. In this guide, we will break down everything you need to know about appendices vs appendixes, including correct usage, common mistakes, and tips to remember the right form.

Quick Answer

The plural of appendix can be either appendices or appendixes.

Appendices is traditionally preferred in British English and is widely used in formal writing worldwide.
Appendixes is more common in American English, especially in general or casual contexts.

Both forms are technically correct, but your choice should depend on your audience and context. For academic and professional writing, appendices is usually safer.

Meaning of the Correct Form

Appendices

The term appendices is the Latin-derived plural of appendix. It is primarily used in formal contexts, such as academic papers, books, or medical literature.

Examples:

The research paper includes several appendices with supporting data. (UK & US)
In the textbook, appendices A and B provide additional exercises. (UK & US)

Notes:

In British English, appendices is overwhelmingly the standard plural.
In American English, appendices is considered more formal or technical, often appearing in academic or scientific writing.

Appendixes

Appendixes is an Anglicized plural form of appendix, and it is more commonly used in everyday American English. While it is less formal than appendices, it is still widely accepted in the US.

Examples:

The book has several appendixes containing additional illustrations. (US)
You can find all the charts in the appendixes at the end of the report. (US)

Notes:

In British English, appendixes is rarely used and may be considered informal or incorrect in academic writing.
In US English, both forms are acceptable, but appendices sounds more professional.

Meaning of the Incorrect Form (If Any)

While both appendices and appendixes are correct, common mistakes often arise due to misunderstanding Latin rules or regional preferences.

Incorrect uses include:

Using appendixes in formal British English texts.
- Incorrect: The thesis contains several appendixes.
- Correct: The thesis contains several appendices.
Using appendices in casual American English may feel overly formal.
- Incorrect in casual context: Please check the appendices for more info.
- Correct in casual US context: Please check the appendixes for more info.

Tip: Always consider your audience and the tone of your writing.

Keyword Comparison / Key Differences

Aspect	Appendices	Appendixes
Origin	Latin	English adaptation
Formal Usage	Academic papers, research, books	Acceptable in casual writing, US English
UK English	Standard plural	Rarely used, considered informal
US English	Formal writing, academic contexts	More common in everyday writing
Examples	“The report includes several appendices.”	“The report includes several appendixes.”

Key Difference:

Use appendices for formal, academic, or professional contexts.
Use appendixes for informal or US-centric everyday writing.

Common Mistakes People Make

Even native speakers sometimes misuse these plurals. Here are the most common errors:

Mixing forms in a single document
- Incorrect: The report has several appendices and appendixes.
- Correct: Stick to one form, depending on audience: either appendices (formal/UK) or appendixes (US/informal).
Using appendixes in UK academic writing
- UK students often use appendixes, which can appear unprofessional.
Confusing with medical usage
- In medicine, appendix often refers to the organ in the body. Its plural can also be appendices, though in casual US usage, appendixes is sometimes seen.
Overcomplicating pluralization
- Avoid inventing forms like “appendixi” or “appendixs.” Only appendices or appendixes are correct.
Misplacing in sentences
- Example of misplacement: The appendix A and B contains data.
- Correct: Appendices A and B contain data.

Correct Usage in Sentences

British English (UK)

The appendices at the end of the dissertation include raw data.
Please refer to appendices C and D for additional charts.
All supplementary materials are listed in the appendices section.

American English (US)

The book contains several appendixes with helpful diagrams.
Refer to the appendixes for more examples.
In the report, appendices provide detailed explanations. (formal/academic US)

Notes:

Always capitalize appendix labels (Appendix A, Appendix B) when referring to specific sections.
Use appendices when writing formally in any region.
Appendixes can be used in informal US English but avoid in UK academic writing.

Tips to Remember the Correct Usage

Think Latin vs English:
- Appendices = Latin plural (formal, UK preferred)
- Appendixes = English plural (informal, US common)
Audience check:
- Writing for UK or international academic audience → use appendices
- Writing for casual US audience → appendixes is acceptable
Mnemonic trick:
- “Ice in appendices → formal, cold, professional”
- “Ex in appendixes → everyday, informal, casual”
Consistency is key:
- Choose one plural form and stick with it throughout the document.
Medical context reminder:
- Human body organ plural can use either form, but appendices is more technical.

FAQs

1. Which is correct: appendices or appendixes?

Both are correct. Appendices is formal and preferred in UK English. Appendixes is common in informal US English.

2. Can I use appendixes in academic writing?

In the US, yes, but appendices is safer and more widely accepted in formal contexts worldwide.

3. How do I pluralize appendix in a medical report?

Both appendices and appendixes are acceptable, but appendices is more professional.

4. Do British writers ever use appendixes?

Rarely. In the UK, appendices is standard in books, research, and professional writing.

5. Is there a difference in pronunciation?

No major difference. Both appendices (uh-PEN-di-seez) and appendixes (uh-PEN-diks-iz) are pronounced according to regional accents.

6. Can I mix appendices and appendixes in one document?

It is strongly discouraged. Always pick one form for consistency.

7. Are appendices always at the end of a book or report?

Yes, they typically follow the main text and include supplementary material like charts, tables, or raw data.

Conclusion

Understanding the difference between appendices and appendixes is simpler than it first appears. The key is to consider your audience and context. Use appendices for formal, academic, and professional writing, especially in the UK and globally. Reserve appendixes for casual US English writing.

By remembering simple tips, keeping consistency, and considering regional differences, you can confidently use either form without hesitation. Whether you are drafting a research paper, writing a book, or compiling supplementary material, using the correct plural will make your writing clear, professional, and credible.