In terms of Section 16(4) of the CGST Act, a registered person is not entitled to claim input tax credit in respect of any supply of goods or services after the earlier of following two events:
(a) Due Date of filing of the return under Section 39 of the Act for the month of
September following the end of financial year to which such invoice or invoice
relating to such debit note pertains, i.e. 20th October;
(b) Furnishing of the annual return. In terms of Section 44, the due date of filing annual return is 31st December following the end of the financial year.
However, in cases of credit in special circumstances like new registration, voluntary registration, etc. the credit will not be available after the expiry of one year from the date of issue of tax invoice.
(ICAI FAQ PUBLICATION 06-09-2017 INPUT TAX CREDIT: FAQ NO.10)