The basic form of a verb is called the infinitive. It normally occurs with the word to as in:
I want to ask you a question.
Verbs may change their spelling according to which tense is being used.
To make the past tense of regular verbs, the ending -ed is added to the infinitive:
I asked her a question.
To make the present participle, the ending -ing is added to the infinitive:
I am asking her a question.
Often there’s no need to make any other spelling changes when you add -ed and -ing to the infinitive but there are some cases when it’s necessary to do so.
Verbs ending with a silent e
If the verb ends with an e that isn’t pronounced, as in bake or smile, then you need to drop this final -e before adding -ed and -ing:
bake, baked, baking.
smile , smiled, smiling.
Verbs ending in -ee, -ye, and -oe, such as free, dye, and tiptoe, do not drop the final -e when adding -ing:
free, freed, freeing.
dye, dyed, dyeing.
tiptoe, tiptoed, tiptoeing.
A few verbs keep the final -e when adding -ing to distinguish them from similar words:
singe becomes singeing rather than singing (which is the present participle of sing).
Verbs ending with a vowel plus -l
If the verb ends with a vowel plus -l, as in travel or equal, then you need to double the l before adding -ed and -ing in British English:
travel, travelled, travelling.
distil, distilled, distilling.
equal, equalled, equalling.
Note: This rule doesn’t apply in American English
Verbs ending with a single vowel plus a consonant
If the verb ends with a single vowel plus a consonant, and the stress is at the end of the word, e.g. refer, then you need to double the final consonant before adding -ed and –ing:
admit , admitted, admitting.
commit, committed, committing.
refer, referred, referring.
If the verb ends with a vowel plus a consonant and the stress is not at the end of the word, you don’t need to double the final consonant when adding -ed and -ing:
inherit, inherited, inheriting.
target, targeted, targeting.
visit, visited, visiting.
If the verb has only one syllable and ends with a single vowel plus a consonant, e.g. stop, then you need to double the final consonant before adding -ed and -ing:
stop, stopped, stopping.
tap, tapped, tapping.
sob, sobbed, sobbing.
If the verb ends with two vowels plus a consonant, you should generally not double the final consonant:
treat, treated, treating.
wheel, wheeled, wheeling.
pour, poured, pouring.
Verbs ending in -c
If the verb ends in -c, e.g. panic, you need to add a -k before adding -ed and -ing, and also -er.
picnic, picnicked, picnicking, picnicker.
mimic, mimicked, mimicking, mimicker.
traffic, trafficked, trafficking, trafficker.