How costly can the delay in filing tax returns be?

First, what are the due dates?
Assessees having income from salary have to file return of income before July 31 of the assessment year. This is the ‘due date’ prescribed in section 139(1) of the Income Tax Act, 1961.
Self-employed businessmen and professionals, and those deriving income from let-out property too have to file their returns by this date.
However, businessmen and professionals with aggregate turnover/annual receipt exceeding Rs 40 lakh (in the case of business) and Rs 10 lakh (in the case of profession) have time up to October 31 for filing their return of income.

Are there any benefits in filing by the due date?
An assessee filing return by the ‘due date’ provided in the statute is eligible to file a revised return if he discovers any omission or wrong statement therein. Time limit for filing revised return is one year from the end of the assessment year or before completion of assessment. No penalty would be levied for filing a revised return on voluntary basis.

So, by filing late, does one lose the revision option?
Yes. If an assessee does not file his return within the ‘due date’ and files his return subsequently, he cannot have the benefit of revising the return, as the return filed beyond the ‘due date’ is treated as ‘belated return’.

Any other advantages of sticking to the deadline?
The taxpayer gets the advantage of carry forward and set off of losses, such as loss from business and loss under the head ‘capital gains’. If the return is filed beyond the ‘due date’ mentioned in section 139(1), these losses cannot be carried and set off against the income of subsequent years.
Yet another advantage of filing return before ‘due date’ is the eligibility for interest on tax refund from April 1 of the assessment year.

Can delay, therefore, be wasteful for ‘refund’ cases?
Yes, because where the return is filed after the ‘due date’, interest on refund is paid only for the period from the month of filing the return to the date of refund. In other words, no interest is paid for the period from April 1 of the assessment year to the date of filing the ‘belated return’.

Do those with ‘nil’ tax liability have anything to fear?
Where the return is filed beyond the ‘due date’, the taxpayer has to pay interest if any, on tax liability existing beyond tax deducted at source (TDS) or tax collected at source (TCS) or the advance tax paid. The question of interest does not arise where tax due for payment is ‘nil’, as would be in the case of most salaried people who pay their taxes through the TDS route. Legally, a taxpayer can file his return before the end of the assessment year without any penalty (however with penal interest under section 234A). Again, the question of penal interest does not arise in the ‘nil’ cases discussed above. For the assessment year 2007-08, return of income could be filed up to March 31, 2008.

How costly can delay in filing IT return be?
Apart from interest and penal interest, there are other implications. If the return is filed after March 31, 2008 but before March 31, 2009 the AO (Assessing Officer) could levy a penalty of Rs 5,000 under section 271F. Even when there is no further tax payable on the income admitted, penalty under section 271F is leviable for the delay. If the return is filed after March 31, 2009 then such return would become an invalid return.

source: HINDU