When do we double the last letter in the past tense?

Question

When do we double the last letter in the past tense? Is there any rule for that?

Answer 1

I'm just citing:

When the verb ends in consonant + vowel + consonant, you have to double the last consonant and then add "ed" to make the Past Simple.

e.g. plan > planned

(Because: l= consonant. a= vowel. n=consonant)

• If you have a verb with more than one syllable, you only double the consonant if the last syllable is stressed.

e.g. re'fer > referred

• In British English the final "l" is doubled, even if the last syllable is not stressed.

e.g. travel > travelled

• If the last letter is "x", you do not double it (because an "x" is in fact two consonant "ks".

e.g. fix > fixed

• If the last letter is "c", you write "ck" instead of "cc".)

e.g. picnic > picnicked

• If the stress is not on the last syllable, don't double

  e.g. de'velop > developed

Of course these rules only apply to regular verbs.

For more information and examples see here - the source of the citing that mentioned above.