What is the procedure adopted for making the assessment under section 144 i.e. best judgment assessment?
Assessment under section 144 (called best judgment assessment) is an assessment carried out as per the best judgment of the Assessing Officer. The other procedures in this regard are as follows:

If the circumstances justifying best judgment assessment (discussed in previous FAQ) are satisfied, then the Assessing Officer will serve a notice on the taxpayer to show cause why the assessment should not be completed to the best of his judgment.
No notice as given above is required in a case where a notice under section 142(1)​ has been issued prior to the making of an assessment under section 144.
If the Assessing Officer is not satisfied by the arguments of the taxpayer and he has reason to believe that the case demands a best judgment, then he will proceed to carry out the assessment as per best of his knowledge.
If the criteria of the best judgment assessment are satisfied, then after taking into account all relevant material which the Assessing Officer has gathered, and after giving the taxpayer an opportunity of being heard, the Assessing Officer shall make the assessment of the total income or loss to the best of his judgment and determine the sum payable by the taxpayer on the basis of such assessment.​