Yes, it is always advisable to file Income Tax Return within the due date to avoid Interest payment for filing after due date.
However if you have missed to file your return you can file belated return before the expiry of one year from the end of relevant assessment year.
E.g. for FY 2014-15, belated Income Tax return can be filed till 31st March 2017.
Please Note : From FY 2016-17, Last date to file Income Tax Return will be the last day of the assessment year, accordingly Last date to file Income Tax Return for FY 2016-17 will be 31st March 2018.