hello,

You should have atleast 75% aggregate marks in boards to be eligible for JEE Main and Advanced . You basically need not to worry about percentage because if you study for JEE Main properly , you can easily score good percentage in boards  You can also have a look for detail eligibility criteria for JEE Main by visiting the link https://engineering.careers360.com/articles/jee-main-eligibility-criteria

The cutoff for 2018-2019 for JEE Main was 74.31 percentile for OBC category .

You can also have a look at the last 5-6 year's cutoff by visiting the link

https://engineering.careers360.com/articles/jee-main-cutoff .