Why Is It 11th, 12th, and 13th — But 21st, 22nd, and 23rd?

English uses 11th, 12th, and 13th because numbers ending in 11, 12, and 13 take “th” as ordinal suffixes. Numbers such as 21, 22, and 23 use “st,” “nd,” and “rd” because their final digits are 1, 2, and 3, and they are not part of the 11–13 exception. This specific rule helps ensure clear communication when describing order or position.

What Are Ordinal Numbers?

Ordinal numbers tell us about the position or order of something in a sequence. Think of them as indicating rank or sequence, such as first place, the second attempt, or the third item on a list. They are different from cardinal numbers (like one, two, three), which simply tell us quantity.

The Basic st, nd, rd, th Rule

For most numbers, the ordinal suffix depends on the final digit. Here’s the general pattern:

• Numbers ending in 1 (except 11) take -st (e.g., 1st, 21st, 31st)
• Numbers ending in 2 (except 12) take -nd (e.g., 2nd, 22nd, 32nd)
• Numbers ending in 3 (except 13) take -rd (e.g., 3rd, 23rd, 33rd)
• All other numbers (ending in 4, 5, 6, 7, 8, 9, 0, or 11, 12, 13) take -th (e.g., 4th, 5th, 10th, 20th)

Here are some common examples of basic ordinal forms:

• 1st = first
• 2nd = second
• 3rd = third
• 4th = fourth
• 5th = fifth
• 10th = tenth
• 20th = twentieth

The 11th, 12th, and 13th Exception

This is where the main confusion often arises. In English, any number that ends in 11, 12, or 13 uses the suffix -th, overriding the basic rule. This means:

• It's 11th, not 11st (eleventh)
• It's 12th, not 12nd (twelfth)
• It's 13th, not 13rd (thirteenth)

This is an important convention in standard English usage.

Why 21st, 22nd, and 23rd Are Different

Numbers like 21, 22, and 23 follow the general rule because they do not fall under the 11, 12, 13 exception. The suffix is determined by their final digit:

• 21st (twenty-first) – ends in 1, and is not 11
• 22nd (twenty-second) – ends in 2, and is not 12
• 23rd (twenty-third) – ends in 3, and is not 13
• 24th (twenty-fourth) – ends in 4, so it takes 'th'

Larger Examples: 101st, 111th, 121st

The rules apply consistently even with larger numbers. You always look at the last two digits of the number to determine the suffix, if those last two digits are 11, 12, or 13. Otherwise, you look at the final single digit.

• 100th = one hundredth
• 101st = one hundred first (ends in 1, not 11)
• 102nd = one hundred second (ends in 2, not 12)
• 103rd = one hundred third (ends in 3, not 13)
• 111th = one hundred eleventh (ends in 11, uses 'th')
• 112th = one hundred twelfth (ends in 12, uses 'th')
• 113th = one hundred thirteenth (ends in 13, uses 'th')
• 121st = one hundred twenty-first (ends in 1, not 11)
• 122nd = one hundred twenty-second (ends in 2, not 12)
• 123rd = one hundred twenty-third (ends in 3, not 13)

Ordinal Numbers in Dates

Ordinal numbers are commonly used when referring to dates. In speech, we often use ordinal forms, saying "June fifth" or "the fifth of June." In written dates, ordinal suffixes may appear in informal or educational contexts, such as "June 5th." However, many formal style guides, particularly in American English, prefer to omit the suffix and simply write "June 5" or "May 1." Always consider your audience and the required formality when writing dates.

Comparison Table

Number	Correct Ordinal	Wrong Form to Avoid	Explanation
1	1st (first)	1th	Ends in 1, not 11.
2	2nd (second)	2th	Ends in 2, not 12.
3	3rd (third)	3th	Ends in 3, not 13.
4	4th (fourth)	4st, 4nd, 4rd	Ends in 4, uses 'th'.
11	11th (eleventh)	11st	Special exception: ends in 11, uses 'th'.
12	12th (twelfth)	12nd	Special exception: ends in 12, uses 'th'.
13	13th (thirteenth)	13rd	Special exception: ends in 13, uses 'th'.
21	21st (twenty-first)	21th	Ends in 1, not 11.
22	22nd (twenty-second)	22th	Ends in 2, not 12.
23	23rd (twenty-third)	23th	Ends in 3, not 13.
111	111th (one hundred eleventh)	111st	Ends in 11, uses 'th'.
112	112th (one hundred twelfth)	112nd	Ends in 12, uses 'th'.
113	113th (one hundred thirteenth)	113rd	Ends in 13, uses 'th'.
121	121st (one hundred twenty-first)	121th	Ends in 1, not 11.
122	122nd (one hundred twenty-second)	122th	Ends in 2, not 12.
123	123rd (one hundred twenty-third)	123th	Ends in 3, not 13.

Common Mistakes to Avoid

Many people make similar errors when writing ordinal numbers:

• Writing 11st, 12nd, or 13rd: Always remember the 'th' suffix for these specific numbers.
• Thinking every number ending in 1 uses 'st': This is only true if the number does not also end in 11 (e.g., 21st, but 11th).
• Thinking every number ending in 2 uses 'nd': This is true unless the number ends in 12 (e.g., 22nd, but 12th).
• Thinking every number ending in 3 uses 'rd': This is true unless the number ends in 13 (e.g., 23rd, but 13th).
• Forgetting the 11, 12, 13 exception in larger numbers: The rule applies to 111th, 112th, 113th, etc., just as it does to 11th, 12th, 13th.
• Writing 'th' for numbers ending in 1, 2, or 3 (when not 11, 12, 13): For example, writing 21th instead of 21st.
• Confusing ordinal numbers with cardinal numbers: Remember, ordinal numbers show order (first), while cardinal numbers show quantity (one).

Practice Exercises

1. Choose the correct form: 11st or 11th.
2. Choose the correct form: 22nd or 22th.
3. Write 13 as an ordinal number.
4. Write 23 as an ordinal number.
5. Write 111 as an ordinal number.
6. Write 121 as an ordinal number.
7. Write 102 as an ordinal number.
8. Explain why 12th is correct but 22nd is also correct.

Answers to Practice Exercises

1. 11th. Numbers ending in 11 always take 'th'.
2. 22nd. The number ends in 2 and is not 12, so it takes 'nd'.
3. 13th. This is an exception; numbers ending in 13 use 'th'.
4. 23rd. This number ends in 3 and is not 13, so it takes 'rd'.
5. 111th. The number ends in 11, so it uses 'th'.
6. 121st. The number ends in 1, and is not 11, so it uses 'st'.
7. 102nd. The number ends in 2, and is not 12, so it uses 'nd'.
8. 12th is correct because numbers ending in 12 always take 'th' as an exception. 22nd is correct because the number ends in 2 and is not part of the 11-13 exception, so it follows the basic rule of using 'nd' for numbers ending in 2.

Frequently Asked Questions (FAQs)

1. Why is it 11th and not 11st?

It is 11th because English ordinal number rules specify that any number ending in 11 uses the 'th' suffix, overriding the general rule for numbers ending in 1.

2. Why is it 12th and not 12nd?

The form is 12th because numbers ending in 12 consistently take the 'th' suffix in standard English ordinal usage, rather than following the 'nd' suffix typically associated with numbers ending in 2.

3. Why is it 13th and not 13rd?

It is 13th because numbers that conclude with 13 are a special case in English ordinal grammar, always using 'th' as their suffix, unlike other numbers ending in 3.

4. Why is it 21st but 11th?

It is 21st because it ends in 1 but is not the specific number 11, so it follows the general 'st' rule. It is 11th because 11 is one of the unique exceptions that always takes the 'th' suffix, regardless of its final digit.

5. What suffix should I use for 111, 112, and 113?

For 111, 112, and 113, you should use 'th', making them 111th, 112th, and 113th. This is because the rule for numbers ending in 11, 12, or 13 applies regardless of how many digits the number has.

6. How do ordinal suffixes work in dates?

In dates, ordinal suffixes like 'st', 'nd', 'rd', and 'th' are often used in spoken English or informal writing (e.g., "May 1st"). However, many formal writing styles, especially in American English, prefer to omit the suffix and simply write the date with the cardinal number (e.g., "May 1").

Practical Summary

Understanding ordinal numbers means remembering two main points: the general rule where 1 takes 'st', 2 takes 'nd', and 3 takes 'rd' (with all others taking 'th'), and the critical exception for numbers ending in 11, 12, and 13, which always use 'th'. By keeping these guidelines in mind, you can confidently write ordinal numbers correctly every time.