The final consonant is preceded by a single vowel: bar → barred
. When there is more than one vowel before the final
consonant, the consonant is not doubled: fail → failed
. When the final consonant is preceded by another consonant,
the consonant is not doubled: bark → barking
The word has only one syllable or has the stress on the last syllable: fit → fitted
, commit → committed
, prefer → preferred.
For words with more than one syllable where the stress does not fall on the last syllable, the final consonant
is not doubled: benefit → benefited, offer → offered.
The suffix begins with a vowel: prefer → preferred
. But if the syllable stress changes because of the addition of the
suffix, then the consonant is not doubled: prefer → preference
. Final consonants are also not doubled if the suffix
begins with a consonant: prefer → preferment.
If the word ends in l or p, then the consonant is usually doubled in Canadian spelling: travel → travelled; worship → worshipped.
Note: American spelling does not follow this rule.