input tax credit on RCM

No ITC beyond September month return of the following F.Y. to which invoice pertains or date of filing of annual return, whichever is earlier.

So, for an invoice of FY 2017-18, RCM self-invoice in this case, ITC can be taken upto 20.10.2018 or 31.12.2018, whichever is earlier.

Sec. 16(4) of the CGST Act, a registered person shall not be entitled to take input tax credit in respect of any invoice or debit note for supply of goods or services or both after the due date of furnishing of the return under section 39 for the month of September following the end of financial year to which such invoice or invoice relating to such debit note pertains or furnishing of the relevant annual return, whichever is earlier