Hi

It is actually very difficult to predict rank now.  Because final rank is based on both the tests namely JEE main and Advanced.  NTA takes best of two.  

Rank is calculated based on percentile. One exam is done and the other test will be conducted in the month of may

However you can calculate approximate rank based on this formula

((100 – P)/100)*N + 1

where P is percentile

And N is total number of candidate which is 8.74 lacks 

Put the nos and get your rank