Last date of itr filing for ay 16-17

DEAR FRIENDS..

I WANT TO KNOW WHAT IS THE LAST DATE OF RETURN FILING FOR AY 16-17....ACTUALLY I AM CONFUSED WHETHER IT WAS 31-3-2017 OR STILL 31-03-2018 AS BELATED RETURN.....SOME OF MY FRIENDS WAS TALKING THAT AFTER 31-3-2017 THERE WILL BE PENELTY ON FILING 16-17 ITR..

ALSO TELL ME FOR WHICH AY THE RULE OF ITR FILING WITH IN A YEAR WILL ENFORCE.