Double letters

When to Double Final Consonants

The final consonant of a word is often doubled when adding -ed, -ing, -er, -est in the following cases:

Double final "b, d, g, l, m, n, p, r and t" at the end of words:
rob - robbing
sad - sadder
big - bigger
travel - traveller
skim - skimming
win - winner
pop - popping
prefer - preferred
hit - hitting

Double these final letters there is the following pattern "consonant - vowel - consonant" at the end of a word. For example: travel - 'vel' v - consonant - e - vowel l - consonant.
Words of more than one syllable have their consonants doubled only when the final syllable is stressed.
begin - beginn ing BUT open - opening
defer - deferr ing BUT offer - offering

When words have more than one syllable and end in 'l' British English always doubles the 'l', even in the case of unstressed syllables. American English, on the other hand, the 'l' is not doubled when the syllable is unstressed.
British English - travelled
American English - traveled