 The constituency is assigned the number 18 of the 40 Lok Sabha constituencies of the state of Bihar by the Election Commission of India.It consists of 6 Assembly segments (constituencies) numbered 105–110 of the Bihar Legislative Assembly, one of which is reserved for Scheduled Caste (SC) candidates in accordance with the Delimitation Order of 2008 implemented on the basis of the Delimitation Act of 2002.The Siwan constituency of the Lok Sabha has no reservation status.