Hello Aspirant,

The calculation of the marks & rank would be difficult based on your percentile. You may calculate your expected rank by this formula

100 - your total percentile score is the percentage  of people ahead of you. 874469 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

You can use the formula given below to predict your rank.

(100 - your total score) X 869010 /100

Good Luck!