Dear Aspirant,

Top 20 percentile means that you are in the top 20% of the students in the board from which you have given your examinations. Your overall result is considered in this process. There is no subject wise analysis for this matter.

Let me explain this you by an example, suppose 100 students have given the exam then for you to be in top 20 percentile means that you score more than 80% of the students who have given the exam.

Your percentile calculations:- (students who have scored more than you/ students who have given the exam) * 100

Note: formula may change in some cases.

Hope this helps.

Some links:- https://engineering.careers360.com/articles/top-20-percentile-of-class-12-boards-for-nits-iiits-and-cftis