The income tax department has urged all taxpayers who have not filed their returns, even by the extended deadline of August 5, 2013, to file at the earliest to "keep away from unavoidable difficulties".

A press release issued Friday said, "Those who missed the deadline of August 5 can still file their I-T returns. If all your taxes are paid and there are no refunds to be claimed it is quite straight and simple. The I-T return can be filed before March 31, 2014. If the return is not filed by that time a penalty of Rs 5,000 will be levied. Those with tax dues will have to pay late fee payable for every month of delay since April 2013."

All those with total income of Rs 5 lakh and above and all those having foreign assets have to necessarily file I-T returns online. More than 1.23 crore taxpayers filed their returns online this year.

Those whose total income is less than Rs 5 lakh can file their returns off-line. While the department gives taxpayers a certain "grace period" to file their returns, there are disadvantages to late filing. Those who file their returns late cannot modify them if there are any mistakes. They also cannot carry forward any short term and long term losses.

The department says it keeps a close watch on transactions and possesses the necessary tools to detect tax evasion. A person defaulting in filing returns of income could be liable for prosecution under Section 276CC of the Income Tax Act, 1961.

Conviction may result in rigorous imprisonment for a term not less than six months but which may extend to seven years and a fine, if the tax liability which has been evaded exceeds Rs 25 lakhs.

Recently, the additional chief metropolitan magistrate, New Delhi, sentenced a taxpayer to six months imprisonment in one assessment year and one year imprisonment in subsequent assessment year for repeating the offence of not filing tax returns.