Can a return be filed after the due date?​​​​​

Yes, if one could not file the return of income on or before the prescribed due date, then he can file a belated return. A belated return can be filed at any time before the end of the relevant assessment year or before the completion of the assessment, whichever is earlier. A belated return attracts interest and penalty.

E.g., In the case of income earned during FY 2020-21, the belated return can be filed up to 31st March 2022. ​​