Have you ever wondered whether the plural of index should be indexes or indices? If so, you’re not alone.
Many people search this question because both forms exist, and the rules aren’t always clear. The confusion comes from history, grammar, and even differences between British English and American English.
Both indexes and indices are correct, but their usage depends on context. In finance and science, indices is more common, while in general writing, indexes is often used.
This article will give you a quick answer, explain the origin of the two words, compare UK vs US preferences, highlight common mistakes, and show how each form appears in everyday examples. We’ll also look at Google Trends data to see which form is most popular today.
By the end, you’ll know exactly when to use indexes and when to use indices—and you’ll avoid confusion in professional writing.
Indexes or Indices – Quick Answer
- Indexes → Standard plural in everyday English (books, websites, databases).
Example: “The book has two indexes at the back.” - Indices → Preferred in mathematics, science, and finance.
Example: “Stock market indices dropped sharply today.”
👉 Rule of thumb: Use indexes for general writing. Use indices in technical, academic, or financial contexts.
The Origin of Indexes or Indices
- Index comes from Latin index, meaning “pointer” or “sign.”
- Latin plurals ended with -ices, so indices was the original form.
- Over time, English developed its own plural system with -es, creating indexes.
That’s why both forms survive today: indices keeps the Latin tradition, while indexes follows modern English rules.
British English vs American English Spelling
Both forms exist in the UK and US, but usage differs slightly:
- British English → “Indices” is more common in academic, scientific, and financial contexts.
- American English → “Indexes” is widely used in everyday writing, while “indices” is still strong in math and finance.
Comparison Table: Indexes vs Indices
| Context | Preferred in British English | Preferred in American English |
| General writing | Indexes | Indexes |
| Mathematics | Indices | Indices |
| Science | Indices | Indices |
| Finance | Indices | Indices |
| Databases/Tech | Indexes | Indexes |
Which Spelling Should You Use?
- Writing for a general audience → Use indexes (easier and more modern).
- Writing for academics or finance → Use indices (expected in professional fields).
- Global/online content → Default to indexes unless your readers are in technical fields.
Common Mistakes with Indexes or Indices
- Mixing the forms in one piece
- ❌ The book has indexes and indices.
- ✅ Choose one consistently.
- ❌ The book has indexes and indices.
- Using “indices” in casual writing
- ❌ My website has indices for topics.
- ✅ My website has indexes for topics.
- ❌ My website has indices for topics.
- Using “indexes” in math/science papers
- ❌ The indices of refraction are shown below.
- ✅ Correct in technical writing: indices.
- ❌ The indices of refraction are shown below.
Indexes or Indices in Everyday Examples
- Email (casual): “I updated the database indexes yesterday.”
- News headline: “Global stock indices fall as markets react to inflation data.”
- Social media post: “New indexes added to improve website speed 🚀.”
- Academic writing: “The study analyzed economic indices across multiple countries.”
Indexes or Indices – Google Trends & Usage Data
Google Trends shows that:
- Indexes is more popular in general English searches.
- Indices spikes in searches related to math, finance, and science.
- Regionally:
- US → “Indexes” leads overall.
- UK, Canada, Australia → “Indices” is stronger in technical contexts.
- US → “Indexes” leads overall.
Usage Comparison Table
| Country/Region | More Popular Word | Context of Usage |
| United States | Indexes | Everyday + databases |
| United Kingdom | Indices | Academic + financial |
| Canada | Both | Context-based |
| Australia | Indices | Science + finance |
| Global average | Indexes | General content + tech |
FAQs on Indexes or Indices
1. Are indexes and indices both correct?
Yes, both are correct. Context decides which to use.
2. Which is more common in finance?
“Indices” is the preferred term in finance worldwide.
3. Can I use “indexes” in a math paper?
No. Use “indices” for mathematics and science.
4. Which is easier for general readers?
“Indexes” is simpler and more familiar to most audiences.
5. Why are there two plurals?
“Indices” is the Latin plural; “indexes” is the English plural.
6. Which should I use for SEO/blogging?
Use “indexes” unless your blog is academic, financial, or scientific.
7. Is one form wrong?
No. Neither is wrong—they are just context-specific.
Conclusion
The debate over indexes or indices comes down to context, audience, and formality. Indexes is the modern, general plural used in everyday English, technology, and casual writing. Indices keeps the Latin tradition and dominates in mathematics, science, and finance.
If you’re writing for a global or general audience, indexes is the safest choice. If your readers are academics, scientists, or investors, indices is the expected form.
By understanding when to use each version, you’ll write with confidence, avoid common mistakes, and adapt to your audience’s expectations. Next time you wonder whether to say indexes or indices, you’ll know exactly which one fits.
