Why is the word permitting spelled with two

The word "permitting" is spelled with two "t"s because it is the present participle of the verb "permit."

The present participle is formed by adding "-ing" to the base form of the verb. Since "permit" ends with a single "t," we add another "t" to make it "permitting."

This is a common rule in English grammar for verbs ending in a single consonant.