As of 2011 India census, Bagaha had a population of 113,012. Males constitute 53% of the population and females 47%. Bagaha has an average literacy rate of 38%, lower than the national average of 59.5%; with 66% of the males and 34% of females literate. 19% of the population is under 6 years of age.
Bagaha is on the banks of the Gandak river. The area is very fertile due to its location in the terai of the Himalayas. The main crops grown here are sugarcane, wheat and rice.
Declaring Bagaha as Police District was one of major steps by Government in order to reduce crime. The road connecting to Patna is now National Highway 28B.
As per orders of Delimitation of Parliamentary and Assembly constituencies Order, 2008, 4. Bagaha (Vidhan Sabha constituency) is composed of the following: Bagaha community development block including
Bagaha nagar parishad; and Bairagi, Sonbarsha, Vairati Bariarwa, Kharhat Tribhauni, Chamawalia and Paikwalia Maryadpur of Sidhaw CD Block.
In the November 2010 state assembly elections Prabhat Ranjan Singh of JD(U) won the 4. Bagaha assembly seat, defeating his nearest rival Ram Prasad Yadav of RJD. Contests in most years were multi cornered but only winners and runners are being mentioned. Purnmasi Ram of JD(U) defeated Narsingh Baitha of Congress in October 2005, and Naresh Ram of RJD in February 2005. Purnmasi Ram representing RJD defeated Kailash Baitha, Independent, in 2000. Purnamasi Ram representing JD defeated Kailash Baitha of SAP in 1995 and Kailash Baitha of BJP in 1990. Triloki Harijan of Congress defeated Purnwasi Ram of LD in 1985 and Melaha Mahto of BJP in 1980. Narsingh Baitha of Congress defeated Kanchan Baitha of Janata Party in 1977.