Hi

Wow congrats that is a great percentile,  with that percentile not only are you qualified for JEE advanced but you can also get into top NIT

To get excat rank it is difficult since the rank is generated based on both the test 

However you can get a approximate rank based on this formula

((100 – P)/100)*N + 1

where p is your percentile

And N is the total number of candidates which is 8.74 lacks 

Plug in the no and gey get your rank

The rank for percentile 99.75 will be around 2190(+-). Note that this is just an estimation. The ranks may vary after JEE Main is again conducted in April 2019. 

Also if a student gives JEE Main both the times then the best score will be considered out of the two. If two students have secured same percentile then the rank will be given higher to student who has scored more marks in Mathematics. So I would suggest you to wait for the final results to be announced by National Testing Agency. 

If you still have any queries feel free to ask in the comment section down below.