Dear Harendr,
Statutory bonus is payable yearly
on the basis of the total salary/wages received by an eligible employee during the entire accounting year.
As you know well, when the salary/wages exceeds the limit of Rs.21000-oo pm, the individual ceases to be an employee for the purpose of the PB Act,1965 and therefore, he is not eligible for bonus from the month his salary exceeded the threshold limit. But, he is eligible for bonus for the entire period during which his salary/wages remained at Rs.21000/= p.m or less within the accounting year.
Applying this rule, if the accounting year of your establishment is the Financial Year ( April - March of next calendar year ), the employee is eligible for bonus for the period from
April to the actual date of October after which his salary became Rs.21200/= due to the hike in D.A.