One of the phenomena that can be observed in the economy is income tax evasion. Its occurrence can be reduced, inter alia, by estimating taxpayers’ taxable income. Tax legislation specifies methods that can be used to this end, however methods other than statutory ones can also be employed. The article aims to evaluate the need for developing tax base estimation methods other than those specified in the legislation by analysing their use by tax authorities. The analysis focuses on cases that the Supreme Administrative Court considered in 2013. Its results show that in nearly 80% of the cases taxable incomes were estimated using methods other than those recommended by law, some of which (e.g. the production method) were never used, one of th...