Listed Company: Mandatory (whether private or Public)
Public Unlisted Company: Internal Audit is mandatory if Turnover is Rs. 200 crore or more, Borrowings is equal to Rs.100 crore or more, paid up share Capital is Rs.50 crore or more, Deposits Rs. 25 crore or more.
Private Unlisted Company: Internal audit is mandatory if Turnover is Rs. 200 crore or more and/or Borrowings is Rs.100 crore or more. Not mandatory to others except mentioned above.