The final paper deals with the topic of interest calculation for commercial loans and credits. It is evident from the legal regulations of the Republic of Croatia that there is a relative and conformal interest rate. The application of the relative and conformal calculation results in a different amount of accrued interest and in the total amount that the debtor must repay to the bank. However, the law does not regulate which interest rate a bank must use when calculating interest on loans, and the aim of this paper is to provide examples of loan or credit repayment method and interest calculation method. Examples of the calculation show the application of relative and conformal interest rates when repaying a loan (credit) in equal annuities and equal repayment quotas, by applying a decursive method of calculation. The results show that there is a difference in the amount of accrued interest when using the relative and conformal interest rates and method of loan repayment. The paper presents the available data on the method of interest calculation and the method of loan repayment used by the Croatian banks.