Rules for Irregular Spelling of Verb Inflections

Doubling of Consonants 

 If the base form ends in a single consonant and the preceding vowel is stressed and spelled with only one letter, double the consonant before adding -ing and -ed

occur/occurring, swim/swimming, ship/shipping 

 If the preceding vowel is unstressed or spelled with two vowels, do not double the consonant

enter/entering, visit/visiting, develop/developing, dread/dreading, 

appeal/appealing, shout/shouting

 If the base form ends in -c, change the -c to -ck

panic/panicking, picnic/picnicking

 There are exceptions with some verbs ending in -l, -m, and -p

travel--traveling or travelling
program--programing or programming
worship--worshiping or worshipping

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Deletion or Addition of -e 

 If the base form ends in an unpronounced -e, drop the -e before adding -ing and -ed inflections

create/creating, type/typing, bake/baking

 For monosyllabic verbs ending in -ye, -oe, or -nge, keep the final -e before -ing, but drop it before -ed

dye--dyeing/dyed
hoe--hoeing/hoed
singe--singeing/singed

 If the base form ends in -ie or -ee, drop the final -e before -ed

die/died, agree/agreed, tie/tied

 If the verb ends in -s, -z, -x, -sh, and -ch, add -e before the -s ending

pass/passes, buzz/buzzes, coax/coaxes, wash/washes, watch/watches

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Treatment of -y 

 If the base form ends in -y, change the -y to -ie

carry/carries, try/tries

 If the base form ends in -ed, change the -y to -i

carry/carried, try/tried

 Following a vowel or preceding -ing, the -y remains

stay/stayed, toy/toying, try/trying, carry/carrying

 If the base form ends in -ie, change the -ie to -y before -ing

die/dying, lie/lying, tie/tying