time limit of rectification of return filed 139-1

An assessee who is required to file a return of income is entitled to revise the return of income under Section 139(5) of Income Tax Act, 1961 originally filed by him to make such amendments, additions or changes as may be found necessary by him. Such a revised return may be filed by the assessee at any time before the end of the relevant assessment year or before the assessment is made whichever is earlier (upto A.Y 2017-18 the return can be revised at any time before the expiry of one year from the end of relevant assessment year or before the assessment is made whichever is earlier).

for rectification, it's 4 years from the end of the financial year in which the order sought to be rectified is passed