Hi Prathamesh !

• For calculating top 20 percentile for different class 12th boards, the marks scored in five subjects - (1) Physics, (2) Chemistry, (3) Mathematics, (4) A language and (5) Any subject other than the above four, is taken into account.

• In case a candidate has taken more than 1 languages as the 4th subject in class 12th, then the language with higher marks will be considered.

• If candidates have taken more than one subject (any subject other than the above four) as the 5th subject in class 12th, then also the subject with higher marks will be taken into account.

• If the marks in a subject are not allotted out of 100, then the total marks for a subject will be scaled (up or down) to 100 so that the total aggregate marks is out of 500.

• In case a candidate passes class XII in 2017, but appears for improvement in one or a few subjects in the year 2018, then the top 20 percentile cutoff for 2017 will be considered. However, if a candidate appears for improvement in all the subjects in 2018, then in this case, best of the two performances (2017 or 2018) will be considered. Thus, candidates appearing for improvement in the next year are advised to take all the 5 papers, as their aggregate marks for the year (in which they appear for improvement) will only be considered only if they appear in the improvement in all 5 subjects.

Visit the link :- https://engineering.careers360.com/articles/top-20-percentile-cutoff-of-class-12-boards-for-iit-admission