hello christo...,

you can use this formula for calculating your jee rank...

100 - your total percentile score is the percentage  of people ahead of you. 869010 are the number of candidates appeared for Jan exam. So rank formula is (100 - your total score) X 869010 /100. If the number of candidates for April exam increased to 1200000 then your final rank shall be (100 - your total score) X 1200000/100.

therefore 44.8x869010/100 will be your jee rank.

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 869010 /100 multiplied by the percentage of people who are ahead of you to arrive at the rank.

hope this helps