ESI contribution is payable on OT but not for EPF. Any payment made not on a monthly basis, such as incentives, performance bonuses, if made, say once in two months or more, ESI is not payable. Certain expenses reimbursed, such as shoe allowance, washing allowance, defray, encashment of leave, bonus/ex-gratia payments, also do not come under the definition of "wages" under the ESI Act.
HC Subbaramu HR Consultant, Bangalore