Dear Aspirant,

NTA (National Testing Agency) conducts JEE Mains all over the nation. After all the attempts of JEE Mains are over ( for example this year 4 attempts are there and it will be over by September 2) when all attempts are over then NTA Announces final result of each candidate in which his/her percentile as well as rank is given and also cutoff percentile to qualify for jee advanced and hence the candidate would come to know whether  he/she has qualified for JEE Advanced.

Expected cutoffs for this year JEE Mains 2021 to qualify  for JEE Advanced 2021 are here :

https://engineering.careers360.com/articles/jee-main-cutoff

Hope this helps.