A chartered accountant's firm is not a shop and hence the Employees Compensation Act may not be applicable to your establishment. If applicable, there is no monthly payment but depending upon the earning capacity of the employee, an amount is fixed and paid. The Act has a schedule which shows how much is the amount payable. Under normal circumstances the amount is decided by the appropriate Authority under the Act, ie, the Commissioner for Workmen's Compensation.
Regards,
Madhu.T.K