To be honest,  its difficult to predict the actual rank or JEE advanced qualifying marks. Neverthless, you may calculate your expected rank by this formula

A percentile is the no.of Candidates who scored better than you in the exam. Going by that, to calculate your JEE percentille, we should use the formula 100 - your total percentile score. Now 869010 Candidates appeared for Jan exam. Going by that, your rank formula  is (100 - your total score) X 869010 /100.

Let's say the number of candidates for April exam increased to 12,00,000 then your final rank shall be (100 - your total score) X 12,00,000/100

At this point in time, it is difficult to predict the JEE Advanced qualifying marks but 85 percentile and above should be an ideal score.