Comparing with than depends on the number of syllables the adjective has:
Adjectives of one syllable:
1. syllable adjectives: add -er to the adjective
My sister is much taller than me.
It's colder today than it was yesterday.
Note: If the word ends: consonant-vowel-consonant, then the last consonant is usually doubled in the comparative.
big - bigger, fat - fatter, hot - hotter
Adjectives of two syllables ending in -y:
2. syllable adjectives ending in -y: change the -y to -ier
She's looking happier today.
This grammar topic is easier than the last one.
Why is everyone else luckier than me?