Hi aspirant

Different boards like CBSE,ICSE,State boards have different "Top 20 percentile".There are certain criteria to calculate top 20%ile.

There are list of boards whose top 20%ile is mentioned in the post which you can check here: https://engineering.careers360.com/articles/top-20-percentile-cutoff-of-class-12-boards-for-iit-admission

For CBSE students it was 424marks last year.This year data is not out yet but will be available soon.

All the best.