Tax Audit = Audit should be done and signed before 30th September.
There is no need to file tax audit report as such however the audit should be completed and signed before 30th. Contravention = Penalty = Rs. 1 Lac
Return Filing = last date 30th September if covered under Section 44AB i.e. Tax audit.
Contravention = Interest u/s 234A,B & C if any tax is payable. Further you will not be able to carry forward any loss of that particular year except unabsorbed depreciaiton.