This is a bit difficult to predict the rank required in to get a seat as cut off keeps changing every year depending upon various factors like number of students that appeared in the jee advanced exam, kind of marks obtained by them , toughness level of the examination , number of seats available for the branch you want etc.
When we go through previous year trend then ,
In round 6 of josaa counselling , 5227 obc rank in jee advanced for obc category closing rank for gender neutral in IIT madras and it was for Biological Sciences (5 Years, Bachelor of Science and Master of Science (Dual Degree))
You can check the same at
So, you need around 5000 obc ncl rank for IIT madras
To have a personalised report on your chances of getting a college you can go through our college predictor, it will give you complete list of colleges which you can get on the basis of the category you belong to, your home state, your gender etc, the link for jee college predictor is provided below
Jee advanced college predictor :-
JEE Advanced College Predictor 2021 - Predict your College
JEE Advanced College Predictor - Know your admission chances in IITs based on your Caste, Gender, Exam Result and Get your JEE Advanced pers ...
Jee main college predictor