Hi

You cannot calculate cutoff using any formulae. It depends on the last candidate taking admission into the particular branch in some college. 

For Eg

Suppose there is a college named A, it has a intake capacity of 100 seats, and say 200 candidates have applied for the seat. The college conducts entrance test called as xyz entrance exam. The college will prepare the merit list based on the the score obtained by the candidate in the entrance exam xyz. Out of 200 students only top 100 students will get admission. say suppose the last candidate i. e candidate securing rank 100 scored 56/100. Then this 56 will be the cutoff for that branch and college.

Likewise EWS reservation will be implemented for the first time in India from this academic year. Hence no previous years cutoff data exist.

Now practically speaking if you are a OBC category student then you cannot avail the EWS reservation facility. This is only for general category.