b420 is a 2005 Hong Kong film directed by Mathew Tang. The film is set in Macau and is a comedy-drama. It is an independent film with a low budget. The tagline of the movie is "Before Twenty... Before Too Old".

b420's title is in reference to "before 20, before too old". According to Tang, "There's a big difference in life from when you're in a school uniform than when you're not." Starring Miki Yeung, Sam Lee, and Ben Hung Jin-Ming, the film tells the story of three adolescents as they become adults and what they think about death, love, and life.