Under Sec.234C(1)(b) of IT Act,1961 an assessee , other than a company, is liable to pay interest for deferment of payment of 1st installment of advance tax by 15 March and 2nd installment by 15 December of a financial year. But, this penal provision does not apply in a couple of cases mentioned in the proviso to clause(b) , where such deferment is due to failure to estimate current income of the financial year. I would like to know if in a similar situation where deferment is due to some other reason not included in this proviso, plea of failure to estimate income will be acceptable to income tax department? That unique situation is elaborated below. A few years ago Govt of India revised pay scales of central Govt employees in pursuance of recommendations of 6th Central Pay Commission. As a result, serving as well as retired employees and officers were entitled to lumpsum amount of arrears, but in some cases it was received towards the end of a financial year. It was not possible to estimate approximate total income of that year before the date of payment of 1st installment of advance tax on 15 Sept. I, a retired officer, however paid total amount of advance tax in one go before 15 March that year after receiving arrears and computing total payable tax. I have taken the plea of 'inability to estimate beyond my control' on this ground in reply to an intimation u/s 143(1) of IT Act, 1961 to pay interest u/s 234C, ibid Will it be tenable or is there any case law in its support?