The percentile score in JEE Main represents the relative performance of a candidate compared to other test-takers in the same session. It is calculated using the formula: Percentile Score = (Number of candidates who scored equal to or less than the candidate / Total number of candidates in that session) × 100. The percentile ranges from 0 to 100 and is normalized to account for differences in difficulty across sessions. The final All India Rank is determined using the best percentile score obtained by the candidate in the sessions they appeared for during that year.