If any person having furnished a return under section 139(1) or in pursuance of a notice issued under section 142(1) [original return], discovers any omission or wrong statement therein, then he may furnish a revised return at any time on or before the expiry of one year from the end of the relevant Assessment Year (AY 2) or before the completion of assessment*, whichever date is earlier. [* Scrutiny assessment or best judgement assessment]
Note 1 : A belated return cannot be revised. [Kumar Jagdish Chandra]
Note 2 : A revised return can further be revised if filed in time allowed. [Dr. N. Srivastava]
Note 3 : A revised return substitutes the original return from the date original return is filed. [Dhampur Sugar Mills Ltd.]
Note 4 : However a return cannot be revised after passing of assessment order u/s 143(3) or section 144.
Note 5 : The date of completion of assessment is date on which assessment order was passed and not the date of service of notice of order upon the assessee.
Note 6 : Loss return u/s 139(3) can also be revised since loss return is treated as return as if filed u/s 139(1).