As per section 139(5), the revised return can be filed before the expiry of one year from the end of the relevant assessment year or before the completion of assessment, whichever is earlier. Thus return of A.Y 2012-13 can be revised till 31st March 2014 or before the completion of the assessment whichever is earlier.
Remember:
1- Revise tax returns within one year from the end of the assessment year or before the assessment. For the financial year 2011-12 one can filed the revised return up to march 2014.
2-You can’t refile your return if income tax department already did the assessment of your return.
3-If you missed any deduction or income in the return you can refile it.
4-If some information come to your knowledge after filing the return you can refile it.
5-The receipt no. & the acknowledgement no. is must for the refiling of the return.
6-No need to pay interest u/s 234A if any tax due, but you have to pay 234B, 234C interest if due.