When you're writing a formal business email, an invoice, or a casual text, stopping to question a spelling is frustrating. If you've ever paused over the number 40 and wondered whether it's spelled forty or fourty, you aren't the only one.
The short answer is simple: forty is the only correct spelling in standard English. Fourty is a common misspelling that appears frequently in student essays, professional drafts, and digital content, but it is entirely incorrect.
Understanding why this spelling trip-up happens—and how other number words follow different patterns—helps you lock down your writing precision. Let's look at why this error persists and how to fix it permanently.
Why Do People Spell It "Fourty"?
The root of this confusion comes down to our natural instinct for phonetic consistency in English. We spell the number 4 as four, so it feels logical to carry that ou cluster over when writing out multiples like fourteen or forty.
English spelling, however, doesn't always follow linear logic. Over centuries of evolution, the letter u dropped out of certain related words while sticking around in others.
Consider this breakdown of related number words:
- Four keeps the u.
- Fourteen keeps the u.
- Fourth keeps the u.
- Forty drops the u.
Because fourteen and fourth proudly display their u, your brain naturally expects forty to do the same. When you type or write fourty, your spellchecker has to step in because your hand is following a false pattern of consistency.
The Etymology Behind the Missing U
Linguists trace the history of English number words back to Old English variants. The number four was originally fēower, and the word for forty was derived from fēowertig.
As Middle English developed into Early Modern English, spelling standardizations began to favor shorter, more phonetic representations for certain decade forms while leaving others untouched. By the time Samuel Johnson and later lexicographers codified modern English spelling rules in the 18th and 19th centuries, forty without the u was firmly established as the standard.
According to the Oxford English Dictionary, the spelling without the u has dominated print and formal writing for centuries, making any variant with an u an orthographic error.
Real-World Impact on Professional Communication
Using the correct spelling matters, especially in professional environments. Typos in numerical words undermine your authority and draw unwanted attention away from your actual message.
Imagine sending a financial statement or a legal contract to a client that reads "fourty thousand dollars." While the numerical digits (40,000) clarify the amount, the written word error signals a lack of proofreading and attention to detail. In high-stakes fields like corporate finance, technical writing, and publishing, minor spelling errors can erode client trust.
Major style guides—including The Chicago Manual of Style and the Associated Press Stylebook—strictly enforce forty. Furthermore, professional journalists and copyeditors view fourty as a red flag during the review process.
Quick Tricks to Never Misspell It Again
If your fingers habitually add that extra u, you can use a few mental tricks to retrain your muscle memory:
- The "For" Trick: Think of the word as the preposition for glued to the suffix ty. For + ty = forty. You wouldn't spell the preposition as four, so don't spell the decade that way either.
- Visual Chunking: Memorize the visual shape of the word without the u. F-O-R-T-Y looks clean and balanced, whereas fourty looks cluttered with extra vowels.
- Contrast with Fourteen: Remind yourself that fourteen needs the u because it's a teenager, but forty is grown up and dropped it.
Frequently Asked Questions
Is "fourty" ever acceptable in British or American English?
No. Neither American English, British English, Canadian English, nor Australian English recognizes fourty as an acceptable spelling. It is classified as a misspelling across all major global dialects.
Why do thirty, fifty, and sixty not have this problem?
Words like thirty, fifty, and sixty don't share a root with a standalone number that ends in an u. Three becomes thirty, five becomes fifty, and six becomes sixty. Only four changes its internal vowel structure when transitioning into a decade.
What about ordinal numbers like "fortieth"?
The ordinal form follows the exact same rule: fortieth is correct, while fourtieth is incorrect. The u remains absent across all derivative forms of the number.
How can I catch this error automatically in my drafts?
Most modern word processors and browser extensions flag fourty immediately. However, if you're typing quickly, you might ignore the red underline. Setting up a custom autocorrect rule in your text editor to automatically swap fourty for forty can eliminate the typo for good.
