British vs American Spelling: The Complete Guide, and Which to Use

Colour or color? Organise or organize? Travelled or traveled? If you learned English from British textbooks and American films, or you write for readers on both sides of the Atlantic, you have probably hesitated over all three. You may also have worried that one of them is wrong.

Neither is. British and American spelling are two standard forms of the same language, each with its own history and its own internal logic. The differences affect only a small share of words, and nearly all of them fall into a handful of patterns. Once you know the patterns, you can choose one system with confidence and stop second-guessing.

This guide explains where the differences came from, sets out every major pattern with examples, covers the traps that catch careful writers, and gives clear advice on which system to use for exams, work and study.

The short answer

Use American spelling when you write for American readers, an American company or an American institution. Use British spelling for readers and institutions in the United Kingdom, Ireland, Australia, New Zealand, South Africa and much of the Commonwealth. For an international audience, either is fine.

Whatever you choose, be consistent within a document. Mixing colour and color in the same report is the one thing that genuinely looks like an error.

Beyond Britain and America

Most of the English-speaking world does not fall neatly into one camp, and it helps to know where your readers stand.

Canada is the best-known mixture. Canadian spelling usually takes the British -our and -re (colour, centre, cheque) alongside the American -ize (organize) and some American vocabulary, such as tire. A Canadian writer who follows neither system exactly is not being careless; that is the Canadian standard.

Australia and New Zealand follow British spelling, generally with -ise. Australia has its own reference dictionary, the Macquarie, and a few American forms have become normal there, most visibly program in every sense. Ireland, South Africa, Nigeria, Kenya, Singapore and Malaysia are broadly British in their official and educational writing.

India is officially British in its spelling, and schools teach it that way. In practice, many Indian writers see American spelling every day in software, films and international business, so mixed writing is common. The Philippines, by contrast, learned English largely through American schooling, and its standard spelling is American.

If you are learning English in one of these places, the local standard is a perfectly good choice. If you are unsure, the school system you learned in is usually the best guide, because those are the forms your hand already knows.

Where the differences came from

For a long time, English spelling was not standardized on either side of the Atlantic. Samuel Johnson's Dictionary of the English Language (1755) did much to settle British spelling, and it kept many forms that reflected French and Latin origins, such as colour and centre.

In the United States, Noah Webster took a different path. His spelling book, first published in 1783, taught generations of American children, and his American Dictionary of the English Language (1828) set out spellings he considered simpler and more American. He favored color, center, defense and traveler. Several of his more radical proposals never caught on, but the ones that did became the American standard.

One common belief is wrong, however. The -ize ending is not an American invention. It comes from the Greek verb ending -izein, and it was used in England for centuries. Oxford University Press still uses -ize in words like organize, a style often called Oxford spelling. The -ise ending became more common in Britain later, partly under French influence. So organize is correct in British English too; it is simply less common in everyday British writing today.

The main patterns

Nearly all British and American differences fall into the patterns below.

A few notes make these patterns much safer to use.

-ise and -ize. Some words end in -ise in both systems, because the ending is part of the root rather than a suffix: advertise, advise, compromise, despise, devise, disguise, exercise, improvise, revise, supervise, surprise, televise. Never change these to -ize. The -yse words are different again: British English always writes analyse and paralyse, even in Oxford spelling, while American English writes analyze and paralyze.

-re and -er. Words where the ending follows a c or g keep -re in American English too, because -er would change the sound: acre, massacre, mediocre, ogre.

Doubled l. This is the most confusing pattern, because it runs both ways. British English doubles a final l before a suffix whenever it follows a single vowel, regardless of stress: travel, travelled. American English doubles only when the last syllable is stressed: travel, traveled, but compel, compelled. Yet in a small group of words, American English has the double l and British English the single one: enroll and enrol, fulfill and fulfil, skillful and skilful, installment and instalment.

Licence and practice. British English uses licence and practice for the nouns and license and practise for the verbs, the same way it uses advice and advise. American English uses license and practice for both.

ae and oe. These matter most in medicine and science: oestrogen and estrogen, haemoglobin and hemoglobin, orthopaedic and orthopedic. British medical writing still keeps the older forms, although some, like medieval, have been simplified on both sides.

-ogue and -og. American English uses catalog and analog widely, but dialogue is still normal in both, except in computing, where a dialog box is standard.

Words that follow no pattern

Some pairs simply have to be learned as pairs.

Three more deserve a note. British English uses programme for a television programme or a plan of events, but program for a computer program. It uses draught for a cold current of air or beer from the tap, but draft for a first version of a document. And judgement is the common British spelling, while British legal writing and American English both prefer judgment. Ageing and aging split the same way.

Traps that catch careful writers

Changing the wrong words. Once people learn that British English uses -ise, they sometimes turn capsize into capsise, or seize into seise. When in doubt, check. Only words with the suffix -ize have a choice.

Assuming derived words behave the same. British colour and humour keep their u in colourful and humourless, but drop it in coloration, humorous, honorary and laborious. American English never has the u. This is one reason spell-checkers are useful here: nobody should be expected to guess honorary.

Forgetting the noun. A British writer who uses organise should also write organisation; one who uses organize should write organization. The noun follows the verb, so the two systems do not share it.

Mixing within a document. This is the most common problem, and the easiest to fix. It usually happens when a writer learned one system at school and reads the other every day. The fix below takes one minute.

Which system to use for exams

IELTS accepts both British and American spelling. You gain nothing by switching to British forms because the test has British roots. Choose the system you already use and keep to it through all your answers. Our guide to spelling in IELTS Writing Task 2 explains how spelling is scored there.

TOEFL also accepts either system. ETS writes its own materials in American English, but British spelling is not marked wrong. The same advice applies: be consistent. See TOEFL Writing and spelling for the details of how responses are scored since the 2026 redesign.

Cambridge English exams, such as B2 First and C1 Advanced, accept American spelling as long as it is used consistently.

Which system to use at work and in study

For academic writing, follow your university, journal or publisher. Many publish a style guide that settles the question, and some British publishers, Oxford University Press among them, use -ize. For business writing, match your organization and your audience. For international organizations, look at their house style: the United Nations and the European Union institutions both write in British-based spelling.

If you are learning English, choose the system that matches where you live, study or plan to work, or the one you already know best. Neither choice limits you. Readers of either system will understand the other without effort.

How to stay consistent

Consistency is a habit, and three small steps build it.

First, set your tools. Word processors, Google Docs and phone keyboards all let you choose English (United States) or English (United Kingdom). Set this once, and the spell-checker will start flagging the other system's spellings as you type.

Second, keep a short list. Write down the fifteen or twenty words you use most often that differ between the systems, in the spelling you have chosen. Behavior, organization, center, program, traveled, defense, analyze and license are common candidates.

Third, do a one-minute check before you send anything important. Search the document for our, ise and ize, re, and ll. Anything that does not match your list stands out immediately.

If you practice spelling regularly, practice in your chosen system. Spelling.School, for example, teaches American spelling but accepts British spellings such as colour and centre as correct, so learners from either tradition can practice without being marked wrong. And if double letters in general give you trouble, our guide to the doubling rule explains the part that both systems share.

What to do next

Decide today which system you will use, and set your word processor and phone to match. Then write your personal list of the words you use most that differ between the two, and keep it where you can see it for a month. After that, you will rarely need it. If you want to practice those words from memory, Spelling.School's free plan is one simple place to start; it uses an American voice and accepts British spellings as correct.

Questions people ask

Is British or American spelling correct?

Both are correct. They are two standard forms of English, and neither is more correct than the other. American spelling is standard in the United States, and British spelling in the United Kingdom, Ireland, Australia, New Zealand and much of the Commonwealth. What matters is choosing the one that suits your readers and using it consistently.

Is organize with a z wrong in British English?

No. The -ize ending is correct in British English and has been used in England for centuries; it comes from Greek. Oxford University Press still uses it, a style known as Oxford spelling. The -ise ending is more common in everyday British writing today, so either is acceptable as long as you are consistent. Words like analyse, however, are always spelled -yse in British English.

Does IELTS accept American spelling?

Yes. IELTS accepts both British and American spelling in every part of the test, wherever you take it. The safe approach is to choose one system and use it consistently, for example always color and organize, or always colour and organise. There is no advantage in switching to British spelling just for the test.

Why do Americans spell words differently from the British?

The differences mostly date from the late 1700s and early 1800s, when Noah Webster promoted simpler spellings in his spelling book and in his American Dictionary of the English Language of 1828. Spellings such as color, center and defense became the American standard. Britain kept older forms that reflected French and Latin origins, largely as recorded in Samuel Johnson's dictionary of 1755.

Is it practice or practise?

In American English, practice is both the noun and the verb. In British English, practice is the noun and practise is the verb, so a British writer would say they practise the piano at their weekly practice. The same pattern applies to licence and license in British English. If you write American English, you only ever need practice and license.

Which spelling should I use for international business?

Either is acceptable for international readers, so the deciding factor is usually your organization's house style or your main audience. If there is no house style, choose the system you know best and use it consistently throughout each document. Setting your word processor to that variety of English will catch most accidental switches.

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