Writing ordinal numbers correctly trips up writers when they hit the transition from teens to decades. If you need to spell 30th, the correct term is thirtieth when written out, or 30th when using figures. Deciding whether to use digits or letters depends entirely on your context, your sentence structure, and the style guide you're following.
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Spelling and Mechanics of Decadal Ordinals
Forming ordinal numbers from multiples of ten follows a predictable linguistic rule in English. You take the base cardinal number—in this case, thirty—and change the ending to reflect its place in a sequence.
When converting thirty to an ordinal, drop the final 'y' and add -ieth. That turns the word into thirtieth. When using numeric digits, you keep the numeral 30 and attach the lowercase suffix th, yielding 30th.
- Cardinal number: Thirty (30)
- Ordinal word: Thirtieth
- Ordinal figure: 30th
Unlike numbers ending in 1, 2, or 3 (like 31st, 32nd, or 33rd), numbers ending in zero rely exclusively on the -th suffix. You never write 30st, 30nd, or 30rd. Mixing up these suffixes is one of the most common errors in professional writing.
Using 30th in Dates and Sentences
Placing ordinal numbers into sentences requires an understanding of syntax and style conventions. How you integrate 30th changes depending on whether it anchors a calendar date, marks a milestone, or indicates a ranking.
Dates and Calendars
When writing out a full date, you can format it in a few different ways depending on your geographic region or publication style.
- American style: October 30th, 2026 or October 30, 2026.
- British style: The 30th of October 2026.
Many modern style guides, including the Associated Press Stylebook, recommend dropping the suffix entirely in formal journalistic dates if the day follows the month directly (e.g., October 30). However, if the ordinal appears on its own or precedes the month, keep the suffix: The 30th of October.
Rankings and Lists
When indicating position or sequence, keep digits or words consistent within your paragraph.
- He finished 30th out of five hundred runners.
- This marks our thirtieth year of continuous operation.
If you're writing formal literary prose, spell out numbers under one hundred. If you're drafting technical reports, financial statements, or instructional lists, figures like 30th offer cleaner readability.
Common Mistakes to Avoid
Writers often slip up when combining ordinals with punctuation or possessive forms. Watch out for these frequent errors:
- The Apostrophe Trap: Never insert an apostrophe before the suffix (writing 30'th is incorrect). The only time an apostrophe belongs near an ordinal is for a possessive noun phrase, such as the 30th anniversary's main event.
- Suffix Confusion: Applying the wrong suffix from neighboring numbers (like writing 30rd because it sounds similar to third).
- Inconsistent Formatting: Switching between digits and spelled-out words in the same sentence (e.g., She placed 30th, but her teammate took twenty-first). Pick one style and stick with it.
Frequently Asked Questions
Is it correct to use superscript for the letters in 30th?
In traditional typography and HTML typesetting, setting the letters as superscript (30^th^) was common for print publications. Today, standard baseline text (30th) is preferred for digital accessibility, readability, and clean screen rendering.
Should I write out thirtieth or use 30th in formal essays?
Most academic style guides, such as the MLA Style Center, recommend spelling out numbers that can be written in one or two words (thirtieth). Save figures like 30th for dates, addresses, statistics, or technical documents.
How do other decade numbers form their ordinals?
All decade numbers follow the exact same rule as thirty. Twenty becomes twentieth (20th), forty becomes fortieth (40th), fifty becomes fiftieth (50th), and so on through the rest of the cardinal numbers.
Does capitalization matter when writing 30th?
Keep the letters lowercase unless the term begins a sentence. Starting a sentence with a numeral is generally poor style; it's better to rewrite the sentence or spell out Thirtieth to maintain proper grammar.
