i got 90.51 percentile .what is my rank

90.51 is a very good score, so before answering your question I would like to Congratulate you and with this rank, you will definitely get admission to a good Institution. Your rank can be predicted between 85k-90k as compared to last year ranks in this percentile.

The formula to calculate the NTA score is:

Percentile Score of a Candidate = 100 x (Number of candidates who secured a raw score (or actual score) EQUAL TO OR LESS than the candidate) / (Total number of candidates who appeared in that session).

Best of luck!!

HELLO
Congratulations for your result and qualifying JEE mains.
since it is very difficult to predict the exact rank but we do have a backup we have a formula to calculate the expected rank that is (100 – Total percentile) x 869010/100.

So according to formula your expected rank for present percentile for January session comes out to be  82469. Now the expected rank might change depending on the no of candidates appearing the april session. For ex if 12 lakh candidate appear the april session then just replace 869010 by 12 lakhs. But if you score above 85 percentile then you have a very decent chance of qualifying jee mains.BUt with present percentile it seems a little difficult for you to get into to 5 NITS
No worries since you have an april attempt left and most importantly baap of the exams i,e Advance which may directly lead you into IIIts.But if you are curious to know that which college you might land into with your percentile then you can use the college predictor link which has following features;
JEE Main 2020 College Predictor

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ALL THE BEST FOR APRIL AND ADVANCE!!