Hi

Admission in IIT is through JEE advanced examination now to be eligible for JEE advanced you need to qualify JEE mains first.

Attempt limit for  JEE MAINS

One  can give JEE Mains entrance  examination  for a maximum of  3 consecutive years  starting from the year of passing 12th board examination.

Now,

JEE Main entrance examination  is conducted twice a year i.e January and April session.

So,  the maximum number of attempts for jee mains entrance examination

= 2 times *3 years

=  6 attempts in total

Now, you are in class 12th so you will be appearing for 12th board in 2021 so you are eligible for both January and April sessions of JEE mains for the year 2021,2022 and 2023

Attempt limit for  JEE ADVANCED

One can give or attempt  JEE Advanced for the maximum of two times and that too in consecutive years.

Thank you