[MOFY]

Doubling the consonant
For most words with a short vowel sound, ending with a single consonant, double the consonant when adding a suffix that starts with a vowel, such as er, ed or ing.
For example:-
mop + ing mopping
big + est biggest
hot + er hotter
For words endling in l after a vowel, double the l before adding er, ed or ing.
For example:-
carol + ing carolling
travel + er travelling
Exceptions:
Some words ending in r, x, w or y are exceptions to the doubling rule
tear + ing tearing
blow + ing blowing
box + er boxer
know + ing knowing

And if your main word has two consonants at the end, or more than one vowel, don't double the consonant.
rain + ing (two vowels a + i) raining
keep + er (two vowels e + e) keeper
break + ing (two vowels e + a) breaking
hang + er (two consonants n + g) hanger

هذي القاعده حصلتها على احد المواقع ,, وكاتب لك الاستثنائات اللي ماتنطبق عليها القاعده

اتمنى افدتكم ,, بالتوفيق