IMPACT OF LATE FILING
Interest: You will be liable for penal Interest u/s 234A @ 1% per month on the amount of tax due from the due date of filing returns.
Carry Forward of Losses: Losses like Business Loss (speculative or otherwise), Capital Loss (short term or long term), and Loss from owning and maintaining race horses are not allowed to be carried forward. Other losses, if any can be carried forward.
Deductions: Deductions u/s 10A, 10B, 80-IA, 80-IAB, 80-IB and 80-IC are not allowed
Revision: Late returns cannot be revised except if it is in pursuance of a notice under section 142(1)
Penalty: A penalty of Rs.5000 may be imposed u/s 271F if belated return is submitted after the end of assessment year (after 31-March-YYYY, e.g. for FY 2007-2008, end of assessment year is 31-March-2009)
You have 3 years to claim a tax refund.
This is measured from the original deadline of the tax return, plus three years. For example, your 2010 tax return is due on April 15th, 2011. Add three years to this filing deadline, and you have until April 15th, 2014, to file your 2010 tax return and still get a tax refund. If you file your 2010 return after April 15th, 2014, then your refund "expires." It goes away forever because the statute of limitations for claiming a refund has closed.