• 3-minute read
  • 26th November 2016

Spelling Tips: Doubling Consonants when Adding a Suffix

The “doubling up” rule (or the “1:1:1 rule”) is one of the few rules in English spelling that is correct most of the time. Given how confusing English can be, we find this reliability oddly comforting. Let’s look at how it works.

What Is the Doubling Up Rule?

The doubling up rule states that, when adding a vowel suffix (e.g., “-ing” or “-ed”) to a single-syllable word that ends with one vowel followed by one consonant, we should double the final consonant. For instance, “dig” gains an extra “g” when changed to “digging.” Additional examples include:

Base Word (Single Consonant)

With Vowel Suffix (Double Consonant)


Starring, Starred, Starry


Running, Runner


Biggest, Bigger

As you can see with “starry” (i.e., lit by stars), “y” is sometimes treated as a vowel for this rule. Other words like this include “sunny,” “blurry,” and “furry.”

The Exceptions

The only universal spelling rule in English is that there’s actually no universal spelling rule in English. As such, we need to mention a few exceptions: words that end in “w,” “x” or “y.” These letters aren’t usually doubled in English, so single-syllable words that end in a vowel plus “w,” “x” or “y” don’t require doubling the final letter when adding a vowel suffix:

Base Word (Single Consonant)

With Vowel Suffix (Double Consonant)


Playing, Player, Played


Snowing, Snowiest, Snowed


Boxing, Boxer, Boxed

Multi-Syllable Words

Things get trickier with words more than one syllable long. Some still require doubling the final consonant when adding a vowel suffix, such as:

Base Word (Single Consonant)

With Vowel Suffix (Double Consonant)


Beginning, Beginner


Regretting, Regretted


Controlling, Controlled, Controller

These are generally words where the final syllable is stressed.

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When the final syllable of a multi-syllable word is not stressed, however, the final consonant is not usually doubled. Examples include:

Base Word (Single Consonant)

With Vowel Suffix (Single Consonant)


Opening, Opened


Listening, Listened, Listener


Happening, Happened

In some cases, whether to double the final consonant depends on the suffix added. “Prefer,” for example, gains an extra “r” in “preferred” or “preferring.” This is because, in both, the final syllable is stressed. However, no doubling is required in “preference,” since the final syllable here is unstressed.

Multi-Syllable Exceptions

There are some words that don’t follow the pattern above, but with which we still double the final letter when adding a vowel suffix to clarify the pronunciation.

With “format,” for example, we typically place the stress on the first syllable. But we still double the “t” when adding a suffix to show that it is pronounced with a short vowel sound. Thus, we pronounce “formatted” as “for-mat-ed,” not “for-mate-ed,” and the double “t” before the suffix helps to clarify this.

There are also some words that end in an “-l” that are conventionally spelled with a single consonant in American English, but that take a double consonant in British or Canadian English. For example:

Base Word

American English (Single Consonant)

British/Canadian English (Double Consonant)


Traveled, Traveling, Traveler

Travelled, Travelling, Traveller


Canceled, Canceling

Cancelled, Cancelling


Modeled, Modeling, Modeler

Modelled, Modelling, Modeller

In other words, multi-syllable words can be tricky! Using the pronunciation to guide your spelling will usually help, but don’t forget to check specific words in a dictionary if you’re unsure whether to double the final consonant when adding a vowel suffix. Likewise, it’s important to proofread your work carefully and double check any words that you’re not 100% sure are spelled correctly.

Comments (28)
30th April 2019 at 07:53
How about words like silhouette and millennium? These aren’t verbs but have double letters.
    30th April 2019 at 08:35
    Hi, AT. I'm not entirely sure I understand your question. It doesn't really matter whether the word is a verb; the post is about adding suffixes to words that end in a consonant. This isn't the case for 'silhouette', so there's no problem there (e.g. when we use it as a verb, the past tense is 'silhouetted'). And I can't think of any situation where 'millennium' would take a suffix, but it would follow the standard rule if it did (i.e. double the final consonant only when the last syllable is stressed). Are you asking more about when to use a double letter in the middle of a word? If so, there's no specific rule for this. It's just a case of trying to remember which words contain a double consonant and always checking your spelling if you're not sure.
    13th January 2021 at 15:30
    How do you double words like "eat" , "red", "aim" , "mad" etc
      13th January 2021 at 16:07
      Hi, Lucky. You do not need to double the letter when adding a vowel suffix if the final consonant in a word is preceded by more than one vowel. This is actually where the name "1:1:1" rule comes from: it applies to words with one syllable and that end in one vowel followed by one consonant. As such, this rule does not apply to "eat" or "aim," both of which are spelled with two vowels before the final consonant. But it does apply to "red" (e.g., the word for something going red is "redden," with a doubled-up "n" in the middle) and "mad" (e.g., "madden").
Cheryl Hailey
30th April 2019 at 19:14
What about the words dress, fall, fill...they are doubled already in the baseword. Are they considered 1-1-1 words?
    1st May 2019 at 07:50
    Hi, Cheryl. The last 1 in the 1-1-1 refers to the final consonant in the word (i.e., it applies to words that end in a single consonant). So "fall," "fill," and similar don't fall under this rule as they end in a double consonant.
      Lucky Udu
      16th January 2021 at 12:38
      What of the word "red, aim, mad etc
      16th January 2021 at 12:41
      Hi, again. We responded in full to your previous comment about these words above, but the summary is that "aim" doesn't follow the pattern so there's no need to double the final consonant when adding a vowel suffix, while "red" and "mad" follow the doubling pattern described in this post (e.g., "maddening," "redden").
Donald Tasca
1st May 2019 at 16:13
The most common instance of doubling is when adding ED or ING to a verb. If a verb ends with consonant -vowel-consonant AND is accented on the last syllable, then you double. e.g., referred. Mnemonic ; CVC+ALS=D If the verb does not end with BOTH, there is no doubling. e.g., wandering, canceled
Noel Commins
21st November 2019 at 18:31
Thank you for these tips. I am only 60 years slow to pick up some rules. May my future correspondence spare the reader, needless grammatical pain.
    22nd November 2019 at 09:13
    Glad to help, Noel! Thanks for your comment.
1st July 2020 at 18:27
CVC+ALS=D; can you please break this down for me? Consonant Vowel Consonant + ALS??= Double. Thanks.
Irma G. Wolfson
22nd July 2020 at 19:35
ALS= Accented Last Syllable
Jelena Gill
3rd September 2020 at 14:33
Imagine that different people have different odds of winning in a certain game of chance and that I want to make those odds more even. In doing so, would I be evening the odds or evenning the odds? Why?
    3rd September 2020 at 15:13
    Hi, Jelena. The correct spelling in that case is "evening," since it's the first syllable we stress when saying "even" (similar to the example of "open" we include in the post).
Lucky Udu
16th January 2021 at 12:45
One of the rules of suffix states that: When a word ends in a short vowel sound and a single consonant, you double the last letter. Examples of this rule are: Fat + er = Fatter Flip + ed = flipped Mud + y = muddy Shop + ed = shopped Swim + ing = swimming But this rule doesn't apply to words like red? redness? and some other words... Why? Pls help out.
    19th January 2021 at 09:38
    Hi, Lucky. As mentioned in our previous replies, it does apply to "red" when using a vowel suffix (e.g., "red" becomes "redden" when you add the suffix "-en"). It does not work with "redness" because "-ness" starts with a consonant, not a vowel.
5th June 2021 at 14:05
You can omit 2 of the 3 'exceptions' if you consider that 'ow' and 'ay' are actually considered 'multi-letter vowel' phonograms. So, that just leaves one exception: X.
    Dan Strychalski
    18th October 2021 at 12:59
    Excellent point. In addition, if we remember that a consonant is a type of sound and not a type of letter, we see why "x" is not really an exception: it represents two consonant sounds.
Nikki O'Brien
22nd September 2021 at 13:16
Cloud - cloudy? Squeak-squeaky? They don't fit this rule. Is it because of vowel teams?
    22nd September 2021 at 17:07
    Hi, Nikki. Thanks for commenting. As we mention in the post, the doubling up rule only applies for words that end with one vowel followed by one consonant, so it won't apply to words with two or more vowels before the final consonant, like "cloud" and "squeak."
    Q H Daryaie
    12th December 2021 at 08:26
    Hi Nikki, what is important for consonant-doubled notion is that the phonetic content of vowel, in fact we double the final consonant when we face with pure vowel or monophthong but your example shows diphthong- OU. This rule just applies to single vowel phonetically.
Dan Strychalski
18th October 2021 at 13:12
Someone on Quora asked why the "t" is doubled in "formatted," "formatting," etc., and I'm stumped. Some Brits apparentnly put stress on the second syllable, but I don't think any Yanks do.
    18th October 2021 at 17:28
    Hi, Dan. "Format" is an exception to the typical rule, with the double "t" in "formatted," "formatting," etc., not reflecting how the stress falls in "format," but instead used to clarify the pronunciation. For example, with a single "t" before the suffix, we might assume the past tense of "format" was pronounced "for-mated" with a long "a" sound (i.e., to sound like "for-mate-ed" rather than "for-mat-ed"). You can see something similar in the word "kidnapped" (i.e., we don't typically emphasize "-napped" in the word, but without the double "p," it might look like it was pronounced "kid-naped" with a long "a" sound). Unfortunately, the English language can be a bit unreliable like this. But thanks for highlighting it! We've thus added "format" as another example of an exception to the usual rule.
8th March 2023 at 03:12
If a word ends in a double -f, or a double vowel before the -f, we usually …..
    12th March 2023 at 12:00
    Hi there! It looks like your comment was cut off halfway – do you want to repost it? We'd be happy to answer any questions you have.
11th April 2023 at 17:39
What do you mean by stressed and unstressed syllable? How do you determine this? If it's an open syllable, is it automatically stressed? Also, I know you mentioned this before, but for the 1:1:1 rule, you state one syllable, one vowel, one consonant to follow the vowel. Two questions: 1) Could you expand this to include one short vowel (as aren't all singular vowels short??) 2) Could you include the 1:1:1 rule to include r-controlled vowels (starry)? Thanks in advance for your input!!
    21st April 2023 at 12:51
    Hi, Teresa. The stress on a syllable is where the emphasis is placed when pronouncing the word; so, to use some examples from the article, “happen” has the stress on the first syllable (pronounced HAPP-en), and “prefer” has stress on the second syllable (pre-FER). And then “pre-FER” becomes “PRE-ference,” with the first syllable stressed. It’s a case of knowing how the word is pronounced as to where the stress is, and saying it out loud will determine this. Open syllables normally contain a long vowel, so these are always stressed (though, as always with English, there are exceptions to this rule, such as “city”). We’re happy to update the article but I’m not sure what you mean by your single short vowel question? We have some examples with “run” and “big” that have single short vowels, but if this is not what you mean, let us know. The 1:1:1 rule just refers to single vowels in general, as long vowels are also included in the rule (e.g., “star”). Also, as we already have included “starry” in our first section What Is the Doubling Up Rule?, do you mean you’d like us to expand separately on syllables with r-controlled vowels?

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