When you need to write down an ordinal number, things get tricky fast. How do you spell 30th? The correct word form is thirtieth, while the numeric short form is 30th. If you drop that crucial middle 'i', you'll end up with common misspellings like thirtyth or thirthy. Let's clear up the confusion once and for all so you don't second-guess yourself in professional emails, birthday invitations, or academic papers.
Understanding how ordinal numbers work in English makes this rule stick. Cardinal numbers tell us how many (thirty), while ordinal numbers show position, order, or rank in a sequence (thirtieth).
The Correct Spelling of 30th in Words
The word is spelled thirtieth.
Notice how the base word thirty changes when we make it ordinal. We drop the trailing 'y' and add '-ieth'. If you just tack '-eth' onto the end of thirty, you get thirtyeth—which looks clumsy and is grammatically incorrect.
Here is the exact phonetic breakdown:
- Syllables: thir-ti-eth (three distinct syllables)
- Pronunciation: /ˈθɜː.ti.əθ/
According to the Cambridge Dictionary, the correct spelling is universally recognized across both American and British English standards, though regional accent variations affect how heavily you pronounce the middle vowel sound.
Numeric Form and Suffix Rules
When you write the digits, the abbreviation is 30th.
English uses specific suffix letters attached to the end of numbers to indicate their ordinal status. We take the last two letters of the spelled-out word—in this case, "th"—and attach them to the numeral.
Here is a quick refresher of the primary suffix patterns:
- 1st (first)
- 2nd (second)
- 3rd (third)
- 4th through 20th (using -th)
- 21st, 22nd, 23rd (returning to -st, -nd, -rd)
- 30th (using -th because thirtieth ends in "th")
People sometimes mistakenly write 30nd or 30rd because they confuse it with twenty-second or twenty-third. Always stick to 30th because the word ends in "-eth".
Common Mistakes to Avoid
Writers stumble over this specific number because of the vowel transition. Watch out for these three frequent errors:
- Dropping the 'i': Writing thirthy or thirtyth is incorrect. You need that 'i' before the 'eth' ending.
- Confusing numerals and words: In formal writing, style guides like The Chicago Manual of Style usually recommend spelling out whole numbers from one through one hundred in narrative text, meaning you would write "thirtieth" instead of "30th" in a book or formal essay.
- Incorrect apostrophes: You don't need an apostrophe before the suffix. Write 30th, not 30'th.
Usage in Sentences
Context dictates whether you use the numeral or the spelled-out word. Let's look at realistic examples.
Dates and milestones require careful formatting. If you're writing a formal invitation, spell it out: "You're invited to celebrate our thirtieth wedding anniversary." For business reports or quick calendar scheduling, the numeral is preferred: "The project deadline is set for November 30th."
Notice how contractions and short sentences keep the prose snappy. It's easy to remember once you tie the spelling back to the root word thirty.
Frequently Asked Questions
Is it spelled thirtyth or thirtieth?
The correct spelling is thirtieth. The incorrect spelling thirtyth happens when people mistakenly keep the 'y' from thirty and add '-th' directly.
Do I need an apostrophe in 30th?
No. Never use an apostrophe before the suffix. Write 30th, not 30'th. Apostrophes are reserved for contractions or possessive nouns, not ordinal number abbreviations.
Should I write 30th or thirtieth in formal writing?
Traditional editorial style guides advise spelling out numbers under one hundred in formal text. Use thirtieth in academic papers, literary works, and formal invitations. Reserve 30th for technical writing, dates, charts, and informal communication.
Why does thirty change to thirtieth?
English orthography drops the terminal 'y' and replaces it with 'i' before adding suffixes that start with a vowel, like '-eth', to prevent awkward double-vowel clusters and maintain smooth pronunciation.
