Hello

It would be difficult to tell you as the cutoff varies every year depending on various factors. However, according to the JAM 2018 cutoff of M.Sc Mathematics in IIT Madras, closing rank was 338 for OBC NCL category candidate.

You can go through the link below and check the previous year cutoff for reference and to have an idea about the rank required-

 https://university.careers360.com/articles/jam-cutoff

Good Luck!