Filing Income tax return after the due date is called belated return. It can be filed before the end of the assessment year. (This period has been changed in Budget 2016.Before Budget 2022. belated return can be filed within one year from end of relevant assessment year)But this change will be applicable from Assessment year 2017-18 and subsequent years.It means if you want to file the return for F.Y 2014-15, the relevant assessment year is 2015-16 and so return can be filed till 31stmarch 2022 and likewise if you want to file the return for F.Y 2015-16 ,the relevant assessment year is 2016-17 and so return can be filed till 31st march 2018.But if you want to file the return for F.Y 2016-17, the relevant assessment year is 2017-18 and so return can be filed till 31st march 2022 only.