hey,

i hope you are doing well , so  after qualifying JEE mains and advanced when you will step out to take admission in NIT and IIT , you will be required to secure a minimum aggregate of 75 percent marks in your 12 grade there is relaxation of 10 percent for SC/ST candidates that is 65 percent , the aggregate will of 5 subjects including physics, chemistry and mathematics , you cannot calculate your aggregate of 6 subjects.

hope this helps

good luck!