Doubling Consonants with Vowel Suffixes  

Because most vowel suffixes are able to replace silent E by preserving the root word’s pronunciation and meaning, we often have to double the final consonant of a root word when it precedes a vowel suffix to avoid confusion. This is especially true for single-syllable root words, but it occurs in certain words with two or more syllables as well.

Doubling the final consonant in single-syllable words

When a single-syllable word ends in a vowel + a consonant, we almost always double the consonant when a vowel suffix is attached; if we don’t, we end up with the suffixed forms of root words that originally ended in silent E (or look as though they did). For example:
Root Word
Correctly Suffixed Words
Incorrectly Suffixed Words
barred, barring
bared, baring
(looks like the root word is bare)
dotted, dotting
doted, doting
(looks like the root word is dote)
fatten, fatter, fattest, fatty
faten, fater, fatest, faty
(looks like the root word is fate)
hopped, hopper, hopping, hoppy
hoped, hoper, hoping, hopy
(looks like the root word is hope)
jogged, jogger, jogging
joged, joger, joging
(looks like the root word is joge)
madden, madder, maddest
maden, mader, madest
(looks like the root word is made)
robbed, robber, robbing
robed, rober, robing
(looks like the root word is robe)
slimmed, slimmer, slimming
slimed, slimer, sliming
(looks like the root word is slime)
stoppable, stopped, stopper, stopping
stopable, stoped, stoper, stoping
(looks like the root word is stope)
trekked, trekker, trekking
treked, treker, treking
(looks like the root word is treke)
This is a reliable rule to follow for single-syllable words that take vowel suffixes. Like most spelling rules, however, there are a number of specific exceptions.

Exception 1: Don’t double a consonant that immediately follows another consonant

Keep in mind that the rule for single-syllable words only applies when the final consonant comes after a vowel: if two or more consonants occur together at the end of the word, we don’t double the final one. For example:
  • back→backed, backing
  • clasp→clasped, clasping
  • dark→darken, darkest
  • herd→herder, herding
  • long→longed, longing
  • opt→opted, opting
  • rest→rested, resting
  • twitch→twitched, twitching

Exception 2: Don’t double X or W

No words in English contain two Xs in a row, and we only have two Ws in a row when they occur in compound words (as in glowworm). This is because X forms two consonant sounds (/ks/), while a final W is technically functioning as a vowel, working with another vowel letter to create a vowel digraph. Thus, when a single-syllable word ends in one of these letters, we don’t double it before a vowel suffix. For example:
Ending in X
Ending in W
ax→axed, axing
coax→coaxed, coaxing
fix→fixed, fixing
tax→taxed, taxing
brew→brewed, brewing
claw→clawed, clawing
glow→glowed, glowing
tow→towed, towing

Exception 3: Don’t double a consonant after two vowels

Two vowels together in the same syllable form a vowel digraph, which makes a specific vowel sound. We don’t need to double a consonant that immediately follows a vowel digraph because the pronunciation of the vowel sound won’t be affected by the vowel suffixes. For example:
Root Word
Correctly Suffixed Words
Incorrectly Suffixed Words
bearable, bearer, bearing
bearrable, bearrer, bearring
deemed, deeming
deemmed, deemming
fouled, fouler, foulest
foulled, fouller, foullest
heatable, heater, heating
heattable, heatter, heatting
gainable, gained, gaining
gainnable, gainned, gainning
oared, oaring
oarred, oarring
shouted, shouter, shouting
shoutted, shoutter, shoutting
wooded, wooden, woody
woodded, woodder, wooddy

Sub-Exception: Words beginning with QU or SQU

The letter U always follows Q in native English words, and at the beginning of a word they create two consonant sounds: /kw/. We don’t treat U like a separate vowel letter in this combination, so single-syllable words beginning with QU (or SQU) have their final consonants doubled before a vowel suffix. Fortunately, there are only a handful of common words in which this is the case:
Root Word
Correctly Suffixed Words
Incorrectly Suffixed Words
quipped, quipping
quiped, quiping
(looks like the root word is quipe)
quitter, quitting
quiter, quiting
(looks like the root word is quite)
quizzer, quizzing
quizer, quizing
(looks like the root word is quize)
squatted, squatting
squated, squating
(looks like the root word is squate)
Note that most single-syllable words beginning with QU or SQU end in more than one consonant (as in quick or squash), have two internal vowels other than U (as in squeak or squeal), or else have a silent E after the final consonant (as in quake or square), which means there is no need to double the final consonant.

Doubling the consonant when the final syllable is emphasized

The rules for doubling final consonants are fairly straightforward for single-syllable words, but they become more complex when a word has two or more syllables. Luckily, there are conventions we can follow for these longer words as well, but they can be trickier to remember because they depend on the pronunciation of the word rather than its spelling alone.
When the final syllable of a multi-syllable word is vocally stressed, we almost always double the final consonant before a vowel suffix. In the examples below, the stressed syllables are shown in bold, with the IPA pronunciation included beneath each root word.
Emphasis on final syllable
Suffixed Words
Emphasis on other syllable
Suffixed Words
beginner, beginning
bickered, bickering
conferrable, conferred, conferring
considerable, considered, considering
forgettable, forgetting
forfeited, forfeiting, forfeiture
incurrable, incurred, incurring
interpreted, interpreter, interpreting
omitted, omitting
opened, opener, opening
preferred, preferring
profitable, profited, profited
transmittable, transmitted, transmitting
traveled, traveler, traveling**
(*Not all vowel suffixes result in a doubled consonant for these words, as we’ll see a little bit later.)
(**See “American English vs. British English” further on.)
Remember, all the other rules we’ve seen so far also apply: in addition to those in an emphasized syllable, we only double single consonants that come after a single vowel, are not followed by silent E, and are not X or W. In all other instances, the final consonant is not doubled. For example:
  • careen→careened, careening
  • decline→declined, declining
  • entreat→entreated, entreating
  • insist→insisted, insisting
  • relax→relaxed, relaxing
But don’t forget our sub-rule about QU—it also applies to words with more than one syllable, meaning we don’t treat U as a vowel. For instance:
  • acquit→acquittal, acquitted
  • equip→equipped, equipping

Exception 1: Doubled consonants in unstressed syllables

Note that there are several words that have primary emphasis on the first syllable but have doubled consonants when taking vowel suffixes. Most of these have a secondary stress on the last syllable, which might be part of the reason why their final consonants are doubled, but this is not always the case.
The situation is made more difficult by the fact that many of these words have variant or accepted alternative spellings in which the final consonant isn’t doubled, and the preference for some of these variants often comes down to regional dialect. This leads to confusing spelling decisions such as kidnaped vs. kidnapped and worshiped vs. worshipped. Unfortunately, we just have to memorize these exceptions:
Emphasis on final syllable
Suffixed Words
Variant/Alternative Spellings
crystalline, crystallize
(Crystalline has only one spelling.)
inputted, inputting
Input, without a suffix, is often used instead of inputted for the past tense and past participle form.
kidnapped, kidnapping
kidnaped, kidnaping
(These variants are acceptable but less common in American English; in British English, only kidnapped and kidnapping are considered correct.)
programmable, programmed, programmer, programming
programed, programing
(Both variants are quite uncommon in modern English. Note that programmable and programmer are considered the only correct forms.)
worshipped, worshipper, worshipping
worshiped, worshiper, worshiping
(These variants are acceptable but less common in American English; in British English, only the double-consonant versions are considered correct.)

Exception 2: Words that change syllable stress

Finally, it’s important to know that adding suffixes can sometimes change the pronunciation of the root word, resulting in stress being placed on a different syllable. When the syllabic stress moves to another part of the word as a result of a suffix, we must use the same spelling rules we’ve looked at already. This is especially common with verbs ending in “-fer.” For example:
Root Word
Double consonant before suffix
(No emphasis change)
Single consonant before suffix
(Emphasis shifted)
(Inferrable is an accepted but uncommon variant.)
Preferable is often pronounced preferable (/prɛˈfərəbəl/), but maintains the same spelling.
(Many dictionaries list referrable as an alternate spelling when the word is pronounced /rɪˈfɜrəbəl/, while referable is shown with the pronunciation /ˈrɛfərəbəl/. However, the word is much more commonly spelled with one R and pronounced with a stress on the second syllable.)

Sub-Exception: Don’t double consonants before “-ic”

Attaching the vowel suffix “-ic” usually results in the word’s emphasis being placed on the syllable directly before it. According to the rules that we’ve seen so far, this should result in final consonants being doubled; however, this suffix is an exception to the rule, and single consonants are never doubled when they come before “-ic.” For example:
  • atom (/ˈætəm/) → atomic (ˈtɑmɪk/)
  • acrobat (/ˈækrəˌbæt/) → acrobatic (/ˌækrəˈbætɪk/)
  • period (/ˈpɪriəd/) → periodic (/ˌpɪriˈɑdɪk/)
  • symbol (/ˈsɪmbəl/) → symbolic (/sɪmˈbɑlɪk/)
Many other suffixes will change the pronunciation of a word without changing the root spelling. To learn more, see the section on Word Stress.

Doubling consonants in American English vs. British English

The rules regarding syllable stress and consonant doubling are all fairly consistent in American English, but there are some notable exceptions that occur in British English—specifically, words ending in L.

Doubling L before vowel suffixes (traveled vs. travelled)

Perhaps the most commonly confused spelling convention is whether or not to double the final L in two-syllable words before a vowel suffix. In American English, we follow the rule that we’ve already established: if the word has an emphasis on the final syllable before the vowel suffix, then the L is doubled. However, most words ending in a single L are stressed on the first syllable, so L remains singular. For example:
Emphasis on first syllable
Suffixed Words
Emphasis on last syllable
Suffixed Words
canceled, canceling
compelled, compelling
equaled, equaling
excelled, excelling
(However, excellent, with two Ls, is pronounced /ˈɛksələnt/.)
labeled, labeling
modeled, modeling
propellant, propelled
traveled, traveling
rebelled, rebellion
In British English, on the other hand, a final L that follows a vowel is almost always doubled before “-ed,” “-er,” and “-ing” regardless of where the stress occurs in the word.
For the sake of comparison, let’s see the preferred American English spellings (with single L) of some common words alongside their preferred British English spellings (with doubled L):
American English
British English
barrel→barreled, barreling
cancel→canceled, canceling
dial→dialed, dialing
duel→dueled, dueling
fuel→fueled, fueling
grovel→groveled, groveling
label→labeled, labeling
model→modeled, modeling
rival→rivaled, rivaling
signal→signaled, signaling
travel→traveled, traveling
barrel→barrelled, barrelling
cancel→cancelled, cancelling
dial→dialled, dialling
duel→duelled, duelling
fuel→fuelled, fuelling
grovel→grovelled, grovelling
label→labelled, labelling
model→modelled, modelling
rival→rivalled, rivalling
signal→signalled, signalling
travel→travelled, travelling
If you’re writing according to the styles of American English and you can’t remember whether to double the final L or not, just check which syllable in the word is being stressed. If you’re writing in British English, it’s a good bet that the L should be doubled.

combating vs. combatting

The word combat has two different pronunciations with different syllabic stress: /ˈkɑmbæt/ (noun) and /kəmˈbæt/ (verb). When we add vowel suffixes to the word, the stress usually remains on the second syllable, but, unlike our previous examples, T remains singular in American English:
  • combat→combated, combating, combative
Dictionaries often list combatted and combatting as acceptable variants in British English, but it is still most common in both styles for T to remain singular before the suffixes.
Note that combative is the only spelling considered correct in both American and British English.

focused vs. focussed

Another consonant ending that often confuses writers is the S in focus. Should it be focused or focussed? Again, there is a difference between American English and British English conventions.
In American English, the S is never doubled before a suffix, so its conjugations are focused, focuses, and focusing. The same rule applies to all forms of the word that have a vowel suffix, as in focusable and focuser.
This is the most common (and preferred) convention in British English as well, but it is not considered incorrect to spell the conjugations with a doubled Sfocussed, focusses, focussing. (Focusable and focuser always take just one S). However, these double-S spellings are much less common and may be seen by some as incorrect, even within the UK.
No matter where in the world you are, it’s best to keep the S in focus singular before a vowel suffix, because it’s always the correct choice.

1. In general, when do we double the final consonant in multi-syllable words?

2. Which of these words would have a doubled consonant before a vowel suffix?

3. Which of the following vowel suffixes never results in a doubled consonant?

4. In single-syllable words, we don’t double the final consonant when it comes after two vowels except:

5. For words that have stress on the first syllable, which consonant is usually doubled in British English, but remains singular in American English?

Get all volumes of The Farlex Grammar Book in paperback or eBook.
Share Tweet