Calanasan, officially the Municipality of Calanasan, (Ilocano: Ili ti Calanasan; Tagalog: Bayan ng Calanasan), (formerly known as Bayag, meaning "slow") is a 1st class municipality in the province of Apayao, Philippines. According to the 2020 census, it has a population of 12,550 people.
Its land area is 1,256.15 square kilometres (485.00 sq mi), making it the largest municipality in the province. Calanasan is the source of the Apayao River which empties into the South China Sea and is the only navigable river in Apayao.