Doubling Rule:

(a) In one-syllable words: One-syllable base words ending in a single consonant immediately following one short vowel must double the final consonant before a suffix beginning with a vowel (e.g., -er, -ing, -est, -ed, y, etc.)

Do not double the final base word consonant if the suffix begins in a consonant (e.g., -ment, -ful, -less, -ness, -ly, etc.)

Examples: big + -er = bigger, but big + -ness = bigness
fret + -ing = fretting, but fret + -ful = fretful

(b) In polysyllabic base words: The above rule applies to the final syllable in a polysyllabic base word if the final syllable is accented.

Examples: begin’ – beginning, beginner
But, o’pen – opening, opened

Again no doubling is necessary when the suffix begins with a consonant as in
forget – forgetting, but, forgetful, forgetfulness.

Final e Rule:

When a base word ends with final –e, drop the e before adding a suffix beginning with a vowel.

Examples: blame - blaming, blamed, but blameless
Time – timing, timer, timed, but timely, timeless

Final y Rule:

(a) When a base word ends in y, change the y to i before adding a suffix;

Examples: heavy – heaviness, heavier; silly – silliest, silliness

(b) Except when the y is preceded by a vowel;

Examples: play – played, playing, played, playful

(c) Except when the suffix begins with an i;

Examples: cry – crying, but cried; baby – babyish; copy – copying, copyist