Interest in the Polish legal system has no legal definition. Under the OECD Model Convention, interest is defined as income from debt claims of all kinds, whether or not secured by mortgage or right to participate in the debtor’s profits, and in particular, income from government loans and income from bonds or debentures, including premiums and prizes attaching to such loans, bonds or debentures. Penalty charges for late payment shall not be regarded as interest within the meaning of this Article.

Tax interpretations and rulings of administrative courts indicate a broad understanding of interest, which also includes commissions, loan fees and cashpooling.