Hi Rayana,
As you know the CBSE announced thier marks calculation method for class 12th on 17th June.
The calculation will be based on performance in class 12th +11th + 10th in a 40:30:30 ratio.
The marks for 12th class will be calculated on the basis of any unit test/ pre- board / mid term exam that you gave this year, will be of 40% weightage .
While the 11th class marks will be will be based on your performance in final theory exams, holding a weightage of 30%.
And class 10th results will be calculated on the basis of your best 3 subjects in final theory exams.

I hope that helps.
Thank you