Hello,

If you are getting 120 score then your percentile will be approximately 90-94. It may differ as the pattern and total score has changed but percentile value is determined how the candidate has performed out of all the candidates. Percentile denoted where you stand in the crowd of candidates who have appeared jee main exam. It shows how many candidates have performed better than you and how you performed better from others from the total candidates.

If your number of candidates ahead you is large then your common rank list will be large. Your categorical rank will get lowered by a factor decided by the board.

for more details check previous year percentage chart:- https://engineering.careers360.com/articles/jee-main-marks-vs-percentile

Hope it helps!