Siddanth,To be eligible for appearing for  JEE Advanced, which is the gateway for admission to IITs, NITs and GFTIs, you need to secure a minimum aggregate of 75% in your boards or be atleast in the top 20 percentile. It is 75 percentile for General Category and 65% for Reserved Categories. 75% or 65% is calculated from the marks scored in Physics, Chemistry, Mathematics, Language and any other subject other than these 4 with the highest marks will be considered. Now your OBC Caste/Community should be listed in the Central OBC list to be considered under OBC-NCL. If your Community doesn't come under Central OBC List, then you shall come under General Category and then you have to score 75% in your 12th. The same rule applies for considering your eligibility for JEE Advanced through JEE Mains as well. And cut offs change every year so you might have to appear for JEE April session to improve our percentile because the qualifying cut off percentile  is expected to be around 75-85 percentile and above. For more information please visit our page: https://engineering.careers360.com/articles/jee-advanced-eligibility-criteria