The paper analyses the type of loan where pricipal is repaid in the form of fixed-amount instalments, at uneven intervals. The rather general approach the author assumes allows him to examine the specific features of this type of instrument, which in turn helps to arrive at precise conclusions, important for both the borrower and lender. In particular, the paper shows that the fixed-instalment repayment is not to the bank's best advantage: when the maturity and number of instalments are determined, the amount of interest on the loan tends to be minimised. Additionally, the paper examines the impact of late payment of the instalments, suggesting ways to reduce the costs involved.