The due date for filing ITRs for an individual is 31July of the following Assessment Year.
For example, you filed a return for P.Y.2015-16,then you have to submit the return electronically within 31st of July,2016 I.e. in the A.Y.2016-17.

The due date for filing ITR for an Individual is 31st July of the following Assessment Year if the Assessee is not subject to Audit Tax.
However, if the Assessee is subject to Tax Audit then the due date for filing ITR is 30th September of the following Assessment Year.  
(In case, the assessee is not subjected to Tax Audit)
For P.Y. 2015-16, you have to submit the return electronically by 31st of July,2016  (A.Y.2016-17).
 
(In case, the Assessee is subjected to Tax Audit)
For P.Y. 2015-16, you have to submit the return electronically by September, 2016 I.e. (A.Y.2016-17).
 
 

31 July in most cases. 30 September in some specific cases.