Hello

Percentile means how much you performed good than total number of candidates who have appeared the test. For example if your percentile is 80 then you performed best for the 80% of total candidates while you scored low for 20% of total candidates who have taken the test.

Mathematically, if 100 students have appeared the exam then you are at 80 then there are 79 students who have performed below than you while 20 students have performed higher than you.

Calculation of percentile totally depends on the number of candidates appears the test so you have take that as the important aspect and prepare accordingly. In JEE main 2019, 99.995-99.976 had rank range 61-350. Marks for 99 percentile was 310 for the same year.

You can see how the competition is! You have to make a good preparation with self-honesty and hardwork. For any more details you can visit the site:- https://engineering.careers360.com/articles/jee-main-marks-vs-percentile

Hope it helps!