Provision relating to income tax return After due date us 139 (1) --effects and carry forward of losses under heads of income

Interest u/s 234A: If there is tax due after deducting advance tax , TDS and self assessment tax then interest will be applicable @1% per month and part thereof up to the date of filing of the return besides interest applicable u/s 234B or 234C. Means this interest is applicable only if there is any tax payable in your return
Loss of Interest on refund:
You may loose interest on refund u/s 244A as delay in filing is attributable to assessee for the period by which you have filed late return.
Audit Report:Person who are liable to get their accounts audited should get the audit report on or before the due date of filing return i.e 30.09.2011.Audit report is only to be prepared and not to be filed any where. In simple word or boldly we can say that if audit report has been signed before 30.09.2011 that is enough, you can file return late and report particulars will be filled when ever you filed your income tax return. This is as income tax circular no 5/2007 point no 6

Revised return :
--Late /belated return can not be revised .
--Some of deductions under subsection 80 are not available for late return.
--Due date of income tax return is related to TDS deposit and disallowance u/s 40a(ia).
--Due date of Income Tax return is related to tax saving u/s 54,54B,54F and some other issues in      capital gain saving account deposit scheme.
Not able to carry forward the losses under various heads:
Not able to carry forward following type of losses if file return after due date
--Speculation loss business loss excluding loss due to un absorbed depreciation and capital exp on      scientific research
--Short term capital loss
--Long term capital loss
--Loss due to owning and maintenance of horse races

However there is no impact on following type of losses even if return is furnished after the due date
--Loss from house property
--Business loss on account of unabsorbed depreciation and capital expenditure on scientific research.
(though delay can be condoned as per circular 8/2001 Dated 16.5.2001 on fulfilling of certain condition) so if you are falls under the ambit of the above points then you should furnish your return up to 31.07.2011 or 30.09.2011 as the case may be without any penalty.