A co-operative housing society is required to file income tax returns before September 30th each year if they have taxable income. They must obtain a PAN number and file ITR-5 as an Association of Persons. Failure to file can result in penalties of Rs. 5,000. Rental income from setting up mobile towers on society premises is taxable, but a 30% standard deduction can be claimed. Transfer premium up to Rs. 25,000 collected from members for flat transfers is not taxable under the concept of mutuality.