​​​​Filing of return is your duty and earns for you the dignity of consciously contributing to the development
of the nation. Apart from this, your income-tax returns validate your credit worthiness before financial
institutions and make it possible for you to access many financial benefits such as bank credits, etc.​​

​​​​​​​​​​Yes, if a person who is required to furnish a return of income under section 139​ and fails to do so within
time prescribed in sub-section (1) , you will have to pay interest on tax due. W.e.f. assessment year 2018-
19, fee as per section 234F is required to be paid if return is furnished after due date. Fee for default in
furnishing return of income will be as follows:

a. Rs. 5000 if return is furnished on or before the 31st day of December of the assessment year;
b. Rs. 10,000 in any other case

However, late filing fee shall not exceed Rs. 1000 if the total income of an assessee does not exceed Rs. 5
lakh.

If a person after furnishing the return finds any mistake, omission or any wrong statement, then return should be revised within prescribed time limit.

A return can be revised before the end of the Assessment Year or before the completion of the assessment; whichever is earlier.

If original return has filed in paper format or manually, then technically it cannot be revised by online mode or electronically.

Revised return can be filed online under section 139(5).  

Amounts paid as advance tax and withheld in the form of TDS or collected in the form of TCS will take the character of your tax due only on completion of self-assessment of your income. This self-assessment is intimated to the Department by way of filing of the return of income. Only then the Government assumes rights over the taxes paid by you. Filing of return is critical for this process and, hence, has been made mandatory. Failure will attract levy of penalty.