Filing of GST Returns is mandatory once the business is registered under GST. Whether the returns shall be filed on monthly basis or quarterly basis depends on the turnover. Mainly, there are two returns to be filed in GST i.e. GSTR-1 and GSTR-3B.
GSTR-3B is a summary of Sales made during the month and Credits claimed during the same period. This return has to be filed on monthly basis irrespective of the turnover
GSTR-1 is a detailed summary of sales made during the month or quarter alongwith the details like Invoice Number, GST Number of the client and other such details. In case of GSTR-1, it needs to be filed on monthly basis if the turnover of the business exceeds Rs. 1.5 crore during the previous year. For those having turnover less than Rs.1.5 crore have an option to file the GSTR-1 on quarterly basis.