They are the same word in two dialects: <strong>mom</strong> is standard in the United States and Canada ("My mom picked me up"), while <strong>mum</strong> is standard in Britain, Ireland, Australia and New Zealand ("I'll ask my mum"). Neither is a misspelling of the other — pick the one that matches your readers.
The core difference
This is a dialect split, not a meaning split. Americans say and write mom, with the vowel of "bomb". Britons say and write mum, with the vowel of "bun". The diminutives follow suit: mommy and mama in the US, mummy in the UK.
Which one your readers expect
- United States, Canada: mom, mommy.
- England (south), Australia, New Zealand, South Africa: mum, mummy.
- Ireland, north-east England, Wales: mam is common in speech and increasingly in writing.
- Birmingham and the West Midlands: mom is used locally in the UK too, which surprises people.
Formal writing in every dialect prefers mother. If a document has to travel — a school letter, an international product page — mother or parent sidesteps the choice entirely.
The test
Go by dialect, not by sound. Writing for the United States or Canada, use mom; for Britain, Ireland, Australia, New Zealand or South Africa, use mum — remembering that in Birmingham and the West Midlands the local spelling is mom, with the same vowel as mum. A rhyme test cannot separate the two there. This matters most in dialogue: a Yorkshire teenager who says "mom" on the page will read as American, and an American child who says "mummy" will read as British.
Capital letter or not?
The same rule applies to both spellings. Capitalise when the word replaces a name: "Thanks, Mum" or "I asked Mom." Use lower case after a possessive: "my mum", "her mom", "his mother's car".
The other meanings of mum
Two catches sit on the British side. Mum is also an adjective meaning silent — "he kept mum about the redundancies", "mum's the word". And in American English, mum is the everyday short form of chrysanthemum, so "a pot of mums" in a US garden centre is flowers, not relatives. Context separates them easily, but the flower sense catches British readers off guard.
A common mistake
Mixing the two inside one piece of writing is the real error. An article that opens with "ask your mum" and closes with "moms everywhere" reads as carelessly edited. Choose a dialect at the start and hold it through the whole page, including the headings and any quoted survey answers you paraphrase.
There is no correctness argument to be had here. Anyone who tells you mom is wrong means it is wrong for British readers, which is a different claim.
Frequently Asked Questions
Is "mom" wrong in British English?
It is non-standard for British readers, except in the West Midlands, where mom is genuinely local. For general UK writing, use mum.
Which is correct, "mummy" or "mommy"?
Mummy in the UK, Ireland and Australia; mommy in the US and Canada. Note that mummy also means a preserved body, so children's writing sometimes uses "mum" to avoid the clash.
What do Canadians say?
Mom, following American usage, though mum appears in parts of Canada with strong British or Irish heritage.