Overtime Calculation - What constitutes Gross Pay - it includes Basic, DA, HRA and all allowances?

Hi All, I read extensively in our forum about overtime, how it is calculated and the criteria. I still have some doubts which I hope to get clarified. My
organisation is into Underwriting services.
When we say Gross Pay - it includes Basic, DA, HRA and all allowances. Does it include the monthly performance bonus and shift allowance? When calculating ESIC, we include Performance bonus and shift allowance for the Gross Pay. Is it the same for Overtime as well. Every month I have a different gross salary because of the varying shift allowance and performance bonus. I am finding difficulty in fixing the Gross salary for calculation.
Kindly help.

Dear Shwetha.Spring,
For overtime work, you are liable to pay wages at the rate of twice his ordinary rate of wages. Shift allowance and monthly performance bonus is not to be included in ordinary rate of wages. The same is not fixed. It is not paid to employees across the board universally, ordinarily and necessarily.
Definition of wages under ESI Act is different. Under this Act, whatever you pay additionally to employee is wages when it is paid at intervals not exceeding two months.
Hope you are clear now.

Thank you Akhil for your inputs.