Number of syllables 

Comparative 

Superlative 

one syllable 

+ -er 

+ -est 

tall

taller

tallest

one syllable with the spelling consonant + single vowel + consonant: double the final consonant:

fat

fatter

fattest

big

bigger

biggest

sad

sadder

saddest

Number of syllables 

Comparative 

Superlative 

two syllables 

+ -er OR more + adj 

+ -est OR most + adj 

 ending in: -y, -ly, -ow
 ending in: -le, -er or -ure
 these common adjectives - handsome, polite, pleasant, common, quiet

happy

happier/ more happy

happiest/ most happy

yellow

yellower/ more yellow

yellowest/ most yellow

simple

simpler/ more simple

simplest/ most simple

tender

tenderer/ more tender

tenderest/ most tender

If you are not sure, use MORE + OR MOST +
Note: Adjectives ending in '-y' like happy, pretty, busy, sunny, lucky etc:. replace the -ywith -ier or -iest in the comparative and superlative form

busy 

busier 

busiest 

Number of syllables 

Comparative 

Superlative 

three syllables or more 

more + adj 

most + adj 

important

more important

most important

expensive

more expensive

most expensive