When you’re writing, it’s helpful to know where your client is from so that you can follow their preferred spelling. American spelling in used in the US, British spelling in used in other English speaking countries, and both versions are common in Canada. If your spell checker is set on American English it will generally not recognize British spellings, and vice versa.
Words that are spelled -or in American English are spelled -our in British English.
Words that end in -er in American English end in -re in British English.
Words that are spelled -ize in American English are spelled -ise in British English.
Similarly, words that end in -yze in American English end in -yse in British English.
Words that end in -ense in American English end in -ence in British English.
In American spelling, words can end in -og or -ogue. In British spelling they always end in -ogue.
Verbs that end in a vowel + -l do not double the “l” when adding suffixes in American English. The “l” is doubled in British English.
The past tense of single syllable words is formed by adding -ed in American English. It is formed by adding -t in British English.
Some words that are spelled with a single vowel in American English use two vowels British English.
Some words are just spelled differently in American and British English: