Spelling: when to double a consonant before adding -ed or -ing to a verb

We add -ing to a verb to form its present participle, and -ed to regular verbs to form the past simple. When doing this, we sometimes double the last letter of the verb, as in these examples:

  • stop ⇒ stopped, stopping
    stoped
    stoping

  • refer ⇒ referred, referring
    refered
    refering

Sometimes, however, we don’t double the last letter, as with the verb visit:

  • visit ⇒ visited, visiting
    visitted
    visitting

To understand this spelling rule, it’s first necessary to know the meaning of vowel and consonant:

vowels = a  e  i  o  u
consonants are all other letters (b  c  d  f  g, etc).

The rule

When to double a consonant before adding -ed and -ing to a verb
We double the final letter when a one-syllable verb ends in consonant + vowel + consonant.* stop, rob, sit stopping, stopped, robbing, robbed, sitting
We double the final letter when a word has more than one syllable, and when the final syllable is stressed in speech. beGIN, preFER beginning, preferring, preferred
If the final syllable is not stressed, we do not double the final letter. LISten, HAPpen listening, listened, happening, happened


In British English, travel and cancel are exceptions to this rule:

travel, travelling, travelled; cancel, cancelling, cancelled.

* We do not double the final letter when a word ends in two consonants (-rt, -rn, etc.):
start – starting, started; burn - burn, burned.

* We do not double the final letter when two vowels come directly before it:
remain – remaining, remained.

* We do not double w or y at the end of words:
play – playing, played; snow - snowing, snowed.

See also:
Spelling: when to double a consonant before adding -er or -est to an adjective >>