Hey,
To calculate the rank, you first need to know the percentage of people ahead of you with higher percentile scores. To calculate that, the formula would be 100 which is the highest score minus your percentile score.
Since the percentile is calculated from a scale ranging from 100 to 0 for each session of examinees, the formula applies the total number of students in the January session which is 8,69,010 /100 multiplied by the percentage of people who are ahead of you to arrive at the rank.
Here's the link below providing you with a better idea of how to calculate your rank based on your percentile.
https://engineering.careers360.com/articles/how-calculate-jee-main-rank-based-on-nta-percentile-score
Hope this helps.
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