13rd or 13th: Which Is Correct?

If you have written "the 13rd of the month" and it looked a little strange, your eye was right to flag it, that ending does not belong on thirteen. The correct ordinal is 13th, with -th, and 13rd is the figure given the wrong suffix. Ordinal numbers, the ones that show order, first, second, third, take a two-letter ending that matches how the spoken word finishes. Third ends in the -rd sound, so the figure is 3rd; but thirteenth ends in the -th sound, so its figure is 13th. The mistake 13rd happens because thirteen contains a three, and the writer borrows the -rd from third without checking how thirteenth is actually pronounced. But you never say "thirteen-third"; you say "thirteenth," ending in -th. That makes 13rd vs 13th a tidy case among commonly confused words: one figure that matches the spoken ordinal, and one that grabs the wrong ending from a lookalike digit. This guide settles it, gives the simple rule for ordinal endings, and shows the trap the teens set so you can avoid it every time.

Is 13rd Correct?

No. 13rd is not correct in any style of English. Every style guide and dictionary treats the ordinal of thirteen as thirteenth, written 13th in figures. A spell- or grammar-checker will flag 13rd, and it appears in no calendar, no formal writing, and no standard usage. It is simply the right number given the wrong two-letter ending.

The form you want is 13th, the ordinal that marks position or a date: the 13th of the month, her 13th birthday, the 13th chapter, finishing 13th in a race. In words it is thirteenth, and the figure 13th is just the numeral 13 with the last two letters of that spoken word, -th, attached. Because thirteenth ends in the -th sound, the figure ends in -th.

It helps to see the small set of endings ordinals can take, because there are only four. A number takes -st when its word ends in first (1st, 21st, 31st), -nd when it ends in second (2nd, 22nd, 32nd), -rd when it ends in third (3rd, 23rd, 33rd), and -th for everything else (4th, 5th, 13th, 100th). The ending always tracks the final sound of the spoken ordinal. Thirteenth ends in -th, full stop, so 13rd is not a variant; it is a mismatch between the figure and the word it stands for.

So if you have written 13rd, the fix is to match the spoken word: 13th.

What Does 13th Mean?

13th, or thirteenth in words, is the ordinal form of thirteen, the version of the number used to show order, rank, or position rather than a plain quantity. Where the cardinal thirteen counts how many, the ordinal thirteenth tells you which one in a sequence: the thirteenth person in line, the thirteenth floor, the thirteenth century.

Its most common everyday use is in dates. "The 13th of July," "Friday the 13th," "born on the 13th," all use the ordinal to pick out a day of the month. It also marks anniversaries and birthdays (her 13th birthday), positions and rankings (he came 13th), and items in an ordered list or series (the 13th item, the 13th amendment). In each case 13th identifies a place in an order.

Both the figure and the word are common, and they mean the same thing: 13th is the numeral shorthand, thirteenth the written-out form. You will see 13th in dates, addresses, and rankings, and thirteenth in more formal prose or when a sentence begins with the number. Whichever you use, the ending is -th, because the spoken word, thirteenth, ends in that sound.

Note too that thirteen belongs to the teens, the run of numbers from eleven to nineteen, and every one of them forms its ordinal with -th: eleventh, twelfth, thirteenth, fourteenth, and so on. This whole band takes -th, which is exactly why the digit hidden inside the word, the three in thirteen, must not drag in the -rd of third. The teens follow their own clean rule, and 13th sits squarely inside it.

Why People Write "13rd"

If the rule is so simple, why does 13rd appear at all? The cause is a single, understandable trap: the digit 3 sitting at the end of 13.

When a writer sees the figure 13 and reaches for its ordinal ending, the eye lands on the final 3 and recalls that 3 by itself is 3rd, with -rd. By a kind of reflex, the -rd gets carried over to the larger number, producing 13rd. The mistake is a pattern-match on the last digit rather than a check of the spoken word. It is the same slip that produces 11st (from the 1 in 11) and 12nd (from the 2 in 12): the writer copies the ending of the lone digit instead of the ending of the actual ordinal.

The trap is sprung by the teens specifically. For most numbers, matching the last digit works fine: 21 ends in 1 and really is 21st, 23 ends in 3 and really is 23rd, because those numbers are said "twenty-first" and "twenty-third." The last-digit shortcut succeeds there, which trains the habit. But the teens break it. Eleven, twelve, and thirteen are not said "ten-first," "ten-second," "ten-third"; they are said eleventh, twelfth, thirteenth, all ending in -th. So for 11, 12, and 13, the last-digit shortcut gives the wrong answer, and 13rd is what it produces.

The cure is to ignore the digit and listen to the word. Say the ordinal aloud, thirteenth, and the ending you hear, -th, is the ending you write. Because no one says "thirteen-third," the -rd has nothing to attach to, and 13th is the only form that matches speech.

Examples in Sentences

Seeing 13th used correctly, next to the genuine -rd numbers and the other teens, makes the pattern clear.

Correct uses of 13th:

• Her birthday is on the 13th of June.
• We live on the 13th floor.
• He finished 13th out of forty runners.
• The 13th century saw great change.
• Friday the 13th is considered unlucky.
• This is the 13th item on the list.

Correct uses of the real -rd numbers and the teens:

• The meeting is on the 3rd. (third)
• Our anniversary is the 23rd. (twenty-third)
• She turned 12th in the rankings, just ahead of him. (twelfth, -th)

Wrong → right corrections:

• The 13rd of the month is a holiday. → The 13th of the month is a holiday.
• He came 13rd in the contest. → He came 13th in the contest.
• We met on the 13rd. → We met on the 13th.
• It is her 13rd birthday. → It is her 13th birthday.

In every use, the correct ordinal is 13th. The -rd ending never belongs to thirteen, because the spoken word ends in -th.

13rd vs 13th: Side by Side

The table sets the correct ordinal against the error and notes the rule behind it.

Aspect	13th	13rd
Correctness	Correct ordinal of thirteen	Incorrect; not used in any style
Spoken word	thirteenth (ends in -th)	no number is said thirteen-third
Ending rule	-th, matching the final sound	wrongly borrows -rd from third
Source of error	—	copying the -rd of the lone digit 3
Same trap	—	also produces 11st, 12nd
Checker behavior	Accepted	Flagged as an error

One column matches the figure to how the ordinal is actually said; the other grabs an ending from the digit at the end of the number. Whenever you write the thirteenth, use -th and you land in the correct column.

How to Remember

The cleanest trick is to say the ordinal out loud and write the ending you hear. Thirteenth ends in the -th sound, so the figure is 13th. There is no -rd sound anywhere in thirteenth, so there is no -rd in the figure.

A second guardrail is to remember the teens as a block: eleventh, twelfth, thirteenth, fourteenth, all the way to nineteenth, every one ending in -th. The teens never take -st, -nd, or -rd. So 11th, 12th, 13th, 14th, and the rest are all -th, no exceptions. If you can hear that "twelfth" plainly ends in -th, then thirteenth does too, and 13rd has nowhere to come from.

It also helps to know exactly which numbers earn -rd: only those said as third, namely 3rd, 23rd, 33rd, 43rd, and so on, where the number really ends in the word third. Thirteen is not one of them; it ends in -teenth. Reserve -rd for the genuine "thirds," keep -th for the teens, and the ending will always be right.

Related Spelling Mixups

13rd belongs to a family of errors where a small ending is chosen by pattern-matching rather than by how the word is actually said or built. If this one tripped you up, two related cases are worth a look. The first is don'ts or dont's, where the question is exactly where a short mark, an apostrophe, belongs when a word is made plural. The second is ect vs etc, where the correct abbreviation depends on the real words behind it rather than on a quick guess. Each makes the same point as 13rd vs 13th: the right ending comes from what the word truly is, not from a hasty resemblance.

Conclusion

13rd vs 13th comes down to matching the figure to the spoken word. The ordinal of thirteen is thirteenth, which ends in the -th sound, so the figure is 13th. The ending -rd belongs only to numbers said as third, such as 3rd and 23rd, and thirteen is never said that way. The error 13rd comes from a single trap: seeing the 3 at the end of 13 and copying the -rd from the lone digit, the same slip that yields 11st and 12nd. The teens defeat that shortcut because eleventh, twelfth, and thirteenth all end in -th. The reliable cure is to say the ordinal aloud and write the ending you hear, and to remember the whole teen band takes -th. Do that, and you will write 13th every time, while 13rd will look as wrong as it is. For more cases where an ending or mark is chosen by resemblance rather than by the real word, browse the full collection of commonly confused words.