time limit for filling application for ractification under section 154

It is within the expiry of 4 years from the end of the financial year in which order sought to be rectified was passed.

The income-tax authority can rectify the mistake on its own motion. AND

The taxpayer can intimate the mistake to the income-tax authority by making an application to rectify the mistake.

IT Authority may rectify any mistake apparent from record under section 154. rectification can be made either by Income tax authority itself on its own motion or if application for rectification is made by assessee. assessee has to file application for rectification before expiry of 4 years from end of FY in which order sought to be amended was passed.