'21th' vs '21st': Which is Correct?

By Amy Gilmore, updated on May 21, 2023

An Need to know which is correct between '21th' vs. '21st?' If so, you are not alone! Writing numbers out can be confusing, no matter your English proficiency or writing experience.

Do not worry, though! When you are done reading this guide with definitions, examples, and grammar rules, you will be an expert on the subject.

If you are in a hurry, I have a quick answer for you. 

Here it is: 

  • '21th' is a grammatical error. 
  • '21st' is the correct numeric abbreviation of twenty-first. 

If you have time to stick around, this lesson will help you write numbers confidently. So, keep reading!

Which is Correct, '21th' vs. '21st?'

I just told you that between '21th' vs. '21st', only the latter is grammatically correct. However, you do not know why 21 has the -st suffix.

Furthermore, remembering the correct suffix to use for twenty-first can be challenging if you do not know why you add -st.

'21st' is an ordinal number that indicates someone or something's position in a race, rank, or order.

An Overview of Ordinals

You ALWAYS add one of four suffixes to ordinals:

  • First = st
  • Second = nd
  • Third = rd
  • Fourth = th

From five to ten, all numbers receive the -th ending, for example:

  • Fifth = th
  • Sixth = th
  • Seventh = th
  • Eighth = th
  • Ninth = th
  • Tenth = th

Eleven through twenty also end in -th, for example:

  • Eleventh = 11th
  • Twelfth = 12th
  • Thirteenth = 13th
  • Fourteenth = 14th
  • Fifteenth = 15th
  • Sixteenth = 16th
  • Seventeenth = 17th
  • Eighteenth = 18th
  • Nineteenth = 19th
  • Twentieth = 20th

After twenty, you hyphenate the tenths and one's place, for example:

  • Twenty-first = 21st
  • Thirty-second = 32nd
  • Forty-third = 43rd
  • Fifty-fourth = 54th
  • Sixty-fifth = 65th
  • Seventy-sixth = 76th
  • Eighty-seventh = 87th
  • Ninety-ninth = 99th

Each tenth digit also ends in -th, for example:

  • Tenth = 10th
  • Twentieth = 20th
  • Thirtieth = 30th
  • Fortieth =40th
  • Fiftieth = 50th
  • Sixtieth = 60th
  • Seventieth = 70th
  • Eightieth = 80th
  • Nintieth = 90th
  • One hundredth = 100th

The suffix added to the digits always corresponds with the last two letters in the written ordinal, for example:

  • Eleventh = 11th
  • Seventy-seventh = 77th
  • One hundred seventy-fifth = 175th
  • Two hundred twenty-fourth = 224th
  • Eight hundred fifty-third = 853rd
  • One thousand five hundred twenty-second = 1,522nd
  • Eight thousand four hundred ninety-eighth = 8,498th
  • One million four hundred fifty-six thousand seven hundred twenty-first = 1,456,721st

When to Use Ordinals Like '21st'

To use ordinals, you need to know when they are appropriate.

So, here are some tips:

  • Use ordinal numbers to indicate digits you provide are a rank or position of the subject.

For example, you may hear a sports announcer say:

Car number 27 just moved into 3rd place with five laps left to the finish line. 

  • Use an ordinal to say that someone is the '21st' person in line, to enter, to pass, or that they are in position 21 in a sequence of other people.

For example, you may hear an airline employee announce:

We would like to welcome aboard the 21st through 25th rows at this time. If you are in rows 21 through 25, please line up to board the airplane

  • Use ordinals when you are giving the number of someone's birthday.

For example, you often see phrases like this one on cards and birthday cakes:

Happy 21st Birthday! I hope you have a special day and a prosperous year! 

  • Use an ordinal to let someone know their position in line.

For example, you often hear automated messages while you are on hold saying:

You are second in line, and your estimated wait time is five minutes. 


You are first in line. As soon as a representative is available, we will connect your call. 

  • Use an ordinal to tell someone what position they need to be in to participate in an activity, opportunity, group, or event.

For example, you might tell someone:

The first 30 people to arrive will be admitted for free, and the 21st person to enter the club will win $1,000 cash. 

Definition of '21st': What Does 'Twenty-First' Mean?

According to the Merriam-Webster Dictionary, the definition of '21st' is:

  • The object assigned number 21 when you are counting a series

It can also mean:

  • A rank position of 21
  • In position 21
  • One of 21 equal portions

Pronunciation: How to Pronounce '21st'

Remembering the correct spellings and suffixes of ordinals is only half the battle. You also have to know how to pronounce them. Many people who have challenges pronouncing words struggle with ordinals.

So, here is a little guide:

  • Use this phonetic spelling to correctly pronounce '21st':

Twen-Tee Fuhr-st

Example Sentences: '21st' and Other Ordinals

With the information above, you should be able to choose the grammatically correct suffix for any ordinal. However, seeing examples of them used in different contexts will help you remember.


  • We were 21st in line to go into the new amusement park, but it still felt like we had to wait forever.
  • I had the 21st-highest GPA in my graduating class. That doesn't seem great, but there were 1,500 students in my class.
  • We were going to meet on Saturday, the 21st, at 3 o'clock. Does that still work for you?
  • Listeners, we have tickets to the sold-out 2023 Music Fest. If you want to win, listen for us to tell you to call in. If you are the 21st caller, you and three friends will be at the show with all-access passes.
  • Do you remember what you did on your 21st birthday? It seems like you wait forever to turn 21. Then, you blink, and you are 40 years old.
  • Everyone wanted to know Janetta's secret. She celebrated her 21st birthday almost 20 years ago, but she didn't look a day over 25.

21st/Other Ordinals

  • Congrats on your 21st Anniversary! I can't believe you have been married for more than two decades, but I look forward to c your 30th, 40th, and 50th anniversaries.
  • When would you like to pay your monthly bill? I like to pay small bills on the 21st, so I can get them out of the way before my rent is due on the 1st.
  • Did Nancy tell you about our trip to the Mediterranean? We are leaving on the 21st of December and returning on the 5th of January.
  • Our first stop will be my family's vineyard in Italy. Next, we will visit Mykonos, Greece, and our third and final destination is Cairo, Egypt.
  • I hope you had a Happy Birthday on the 5th. I am sorry I missed your party on the 8th, but I had an early morning meeting on the 9th.

The Last Word on Which is Correct, '21th' vs. '21st'

The next time you need to choose between '21th' vs. '21st', you should have no problem picking the right one. Just to be sure, let's recap what you learned:

  • '21th' is incorrect and ALWAYS an error.
  • The correct ordinal form of 21 is '21st.'
  • Use '21st' and other ordinals to show the position, rank, or order of something.

If you get caught up on these terms in the future, come back to this guide to review the information. Before you go, you should also take a look at a few of the other confusing word posts. They are an excellent way to expand your vocabulary and learn how to use commonly mistaken phrases and words.

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Written By:
Amy Gilmore
Amy Gilmore is one of the lead freelance writers for WritingTips.org. She has been a professional writer and editor for the past eight years. She developed a love of language arts and literature in school and decided to become a professional freelance writer after a demanding career in real estate. Amy is constantly learning to become a better writer and loves sharing tips with other writers who want to do the same.

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