a.         For most verbs, a gerund is formed by adding –ing to the simple form of the verb.

Examples:  Watch – watching, read – reading

b.         If the simple form of the verb ends in a single “e,” a gerund is formed by dropping the “e” and adding –ing.

  Examples:  live – living, drive – driving

c.         If the simple form of the verb ends in “ie,” a gerund is formed by changing the “ie” to “y” and adding –ing.

Examples:  die – dying, lie – lying

d.         If the simple form of a one-syllable verb ends in a consonant + a single vowel + consonant, a gerund is formed by doubling the final consonant and adding –ing.

Examples:  stop – stopping, swim – swimming

e.         If the simple form of a verb with 2 or more syllables ends in a consonant + a single vowel + a consonant, a gerund is formed by doubling the final consonant only if the stress is on the final syllable. 

Examples:  begin – beginning (stress is on second syllable), but visit – visiting (stress is on first syllable)

Note:  The final “l” is doubled in British English (travel – travelling), but not in American English (travel – traveling).

f.         If the simple form of the verb ends in “w”, “x”, "y" or “z,” the final consonant is not doubled when adding –ing.

  Examples:  fix – fixing, snow – snowing, play – playing