If the Pokemon you're facing has multiple types - such as the Flying / Normal Type Pidgey and its evolutions - then it'll take the average of those two Catch Bonuses. The question is, plus three ...
So, how do you get there quickly? Be recycling your duplicates. Pokémon like Rattata and Pidgey and Weedle — Pokémon that you run into frequently, that cost very few candy to evolve.