Both spellings are correct — the difference is regional. Categorize, with a z, is the standard spelling in American English. Categorise, with an s, is the standard spelling in British English. The meaning, pronunciation, and grammar are identical, so simply choose the spelling that matches your audience and use it consistently.

Key Takeaways

• Categorize is the American English spelling; categorise is the British English spelling.
• Both words mean the same thing: to sort people or things into groups or classes.
• Both are pronounced the same way: KAT-ih-guh-rize.
• The real spelling error to watch for is “catagorize” — with an extra “a.” That one is always wrong.

What Does “Categorize” Mean?

To categorize means to put people or things into groups, based on what they have in common. When you categorize something, you are saying which set or class it belongs to.

You do this every day. A librarian categorizes books by genre so readers can find them. Scientists categorize animals and plants into families and species. A budgeting app categorizes your spending into food, travel, and bills so you can see where your money goes.

The word can also mean to describe or label someone in a simple way, as in “It is unfair to categorize all teenagers as careless.” In this sense, it is about putting a label on a person, not just sorting objects.

Categorize is a transitive verb, which means it always needs an object — you categorize something. Dictionaries date it to around 1700, built from the noun “category” plus the verb-making ending -ize. That ending is exactly where the spelling split with British English begins.

Categorize vs. Categorise: The Only Difference Is One Letter

Here is the honest truth: there is nothing to choose between the two words except spelling.

	Categorize	Categorise
Used in	United States	United Kingdom, Australia, New Zealand
Ending	-ize	-ise
Meaning	Sort into groups or classes	Sort into groups or classes
Pronunciation	KAT-ih-guh-rize	KAT-ih-guh-rize
Example	Please categorize these files.	Please categorise these files.

Categorise is not a misspelling, and categorize is not slang or a typo. Dictionaries list categorize as the main form and categorise as the British variant — Collins adds the note “in BRIT, also use categorise,” and Dictionary.com labels categorise “especially British.” The same one-letter pattern shows up in words like standardize/standardise, organize/organise, and recognize/recognise.

Be careful, though: a few websites claim that categorize is a noun and categorise is a verb. That is simply not true. Both spellings are verbs with the same meaning. The noun form is “categorization” (or “categorisation” in British spelling).

Which Spelling Should You Use?

Use the spelling your readers expect. That one rule settles almost every case.

Writing for an American audience

Use categorize. It is the form listed first in Merriam-Webster, and it matches what American style guides like the AP Stylebook and The Chicago Manual of Style expect. To an American reader, categorise can look like a typo, even though it is a perfectly real word.

Writing for a British audience

Use categorise for general readers — it is the everyday British choice, and the same is true in Australia and New Zealand. But categorize is not wrong in Britain. Oxford spelling, used by Oxford University Press and many academic publishers, keeps the -ize ending, so British readers meet categorize in books and journals all the time.

Writing for school, work, or data

This word shows up constantly in essays, reports, spreadsheets, and software. In those settings, consistency matters more than the choice itself. If a report says “categorized” in one table and “categorised” in the next, readers notice the clash, not the spelling. Pick the variety of your school, company, or client, and apply it everywhere — labels, headings, and file names included.

Why does English have two spellings?

The -ize ending comes from the Greek ending -izein, carried into Latin as -izare. French later softened that ending to -iser, and British English picked up the French-style -ise for many verbs. American spelling kept the older -ize. So the z form is not a modern American invention — it is actually the more original one.

Every Word Form: Categorize and Categorise Side by Side

The s/z swap runs through almost every form of the verb, including the noun built from it.

Form	American English	British English
Base verb	categorize	categorise
Third person	categorizes	categorises
Past tense	categorized	categorised
-ing form	categorizing	categorising
Noun (process)	categorization	categorisation
Adjective	uncategorized	uncategorised

Some related words never change, which makes life easier. Category, categories, categorical, and categorically are spelled exactly the same in American and British English.

Spellcheckers accept all of the verb forms above, so the “correct” one is simply the one that matches the rest of your document.

Examples in Sentences

American spelling (categorize):

• The teacher asked students to categorize the words by their meanings.
• Our app categorizes each expense as soon as you enter it.
• He categorized the photos into folders by year.

British spelling (categorise):

• The shop categorises its books by age group.
• Staff categorised the complaints before the meeting.
• It is hard to categorise a film that mixes comedy and horror.

Both sets of sentences are correct. What would be wrong is mixing them, like writing “she categorised the data” in one paragraph and “we will categorize the rest” in the next. Together they clash; apart, each is fine.

Common Mistakes to Avoid

1. Writing “catagorize” or “catagorise.” The extra “a” after “cat” makes both forms wrong in every variety of English. The word starts “cate-,” like “category.”
2. Believing one spelling is a noun and the other is a verb. Both are verbs. The noun is categorization/categorisation.
3. Treating categorise as a typo. It is standard British spelling, listed in every major dictionary.
4. Thinking categorize is banned in the UK. Oxford-style publishers and British academic writing use it regularly.
5. Mixing the two forms in one essay, report, or website. This inconsistency is the only real error here.

The 10-Second Rule

If your audience is American, write categorize. If your audience is British, write categorise. Then stay consistent, and double-check that you have not typed “catagorize” anywhere. That is genuinely all there is to it.

And when you are editing someone else’s work and both forms appear, standardize to the audience’s variety instead of “correcting” everything to your own habit.

Frequently Asked Questions

Is it categorize or categorise?
Both are correct. Categorize with a z is the standard spelling in American English, and categorise with an s is the standard spelling in British English. Neither one is a mistake — choose based on your audience.

How do you spell categorize in British English?
The everyday British spelling is categorise. However, categorize is also accepted in Britain under Oxford spelling and appears often in academic and scientific publishing.

What is the past tense — categorized or categorised?
It follows your base spelling. American writers use “categorized,” as in “she categorized the files.” British writers use “categorised,” as in “she categorised the files.”

How do you pronounce categorize and categorise?
They sound identical: KAT-ih-guh-rize (/ˈkæt.ɪ.ɡə.raɪz/). The s and z spellings make no difference to the pronunciation at all.

Is “catagorize” a correct spelling?
No. “Catagorize” (and “catagorise”) with an extra “a” is a common misspelling. The correct forms are categorize and categorise, matching the start of the word “category.”

What is the noun form — categorization or categorisation?
Both exist, and they follow the same regional pattern. American English uses “categorization,” while British English usually uses “categorisation.” Words like category and categorical, however, are spelled the same everywhere.

Conclusion

Categorize vs categorise? You are not choosing between a right word and a wrong one — both are correct, standard English, and they mean exactly the same thing. Categorize belongs to American English, and categorise is the everyday British form.

Choose the one your readers use, apply it consistently, and watch out for the one true error: the extra “a” in “catagorize.” If you write for a mixed international audience, categorize is the safer default, because no reader anywhere will mistake it for a mistake.