This discussion clarifies the mandatory filing requirements for GSTR 9C. It explains that businesses with an aggregate annual turnover exceeding ₹5 crore (for FY 2018-19 onwards, previously ₹2 crore) must file this reconciliation statement. If your turnover is below this threshold, filing GSTR 9C is optional but can be done voluntarily.
Every registered person whose aggregate turnover during a financial year exceeds 2 crore rupees shall get his accounts audited as specified under sub-section (5) of section 35 of the CGST Act, and shall furnish a copy of the audited annual accounts and a reconciliation statement, duly certified, in FORM GSTR-9C.
This Limit of 2 crore is increased to 5 crores for F.Y 2018-19.
So, if your Turnover is more than this limit than, GSTR 9C is mandatory. If turnover less than this limit, than its optional, you can file voluntary, if you want.
Note : Aggregate turnover normally means "total turnover excluding GST"