Hello Aspirant,
As you have not mentioned the course in which you are seeking admission in IIT Madras or IIT Bombay so it is little bit difficult to guide you an accurate information but if we go through your profile then it shows that you are an engineering aspirant so you might be interest in admission to B.Tech course. If I am wrong then please correct me in the comment section below I would be helping you further with relevant information.
Now for admission to B.Tech courses in any of the IITs is taken solely on the basis of rank secured in JEE-Advance. JEE-Advance is an engineering entrance examination conducted by any of the IITs in rotation every year for admission to B.Tech courses offered in IITs. To be eligible for JEE-Advance one needs to sit for JEE-Main which is conducted four times in an year by NTA and should qualify in JEE-Main with qualifying cut-off percentile which are expected for 2021 like :-
Note that in above table it is not the actual cut-off for JEE-Main 2021 but expected on the basis of previous year's analysis. You can check out previous year's cut-off trends from the link given below :-
https://engineering.careers360.com/articles/jee-main-cutoff
For complete details about JEE-Advance kindly check out the link given below :-
https://engineering.careers360.com/exams/jee-advanced
I hope this information helps you.
Good Luck!!
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