The cut off varies year wise and there is nothing announced for 2018 cut off but as per previous year information if you get 150+ then chances should be there in lower NITs. So I would sugest you to try to get 230-270 if you wish to get seat in top NITs and in top branches like CS, ME, ECE, EE etc.

For reference you can go through the below previous year cut off as this would be giving you the rough idea about the same -

NITs cut off

Good Luck!!!