The number is arrived from the myth that people need to file 3 returns per month and one at the end of the year. Another article[1] quotes Revenue secretary say

The number is arrived from the myth that people need to file 3 returns per month and one at the end of the year. Another article[1] quotes Revenue secretary saying "There is only one return with three parts, out of which first part filed by dealer and two other parts auto populated by computer." So effectively 12 + 1 returns every year EDIT: A tweet from the secretary himself: https://twitter.com/adhia03/status/881428128177901570 https://twitter.com/adhia03/status/881428128177901570 [1] http://indianexpress.com/article/business/economy/revenue-secretary-busts-8-gst-myths-says-implementation-and-execution-will-be-transparent-4732070/ http://indianexpress.com/article/business/economy/revenue-se...