The subject of the study is CIT tax relief regulated by Article 15cb of the CIT Act (known as interest relief). This relief provides for additional tax deductible expenses, even though no expenses were incurred in the amount of multiplication result of additional capital contribution made to the company and/or profit contributed to the company’s reserve capital or supplementary capital and NBP’s reference rate applicable on the last working day of the year preceding the fiscal year increased by 1 percentage point. The author presents eleven interpretation doubts that arose during the four years of the relief being in force. Most of the doubts concerned individual tax decisions issued by the Director of the National Tax and Customs Information Office. The author subjects these interpretations to a critical assessment, presenting his own opinion, sometimes different from that of the tax authorities.