Abstract: Probabilistic model checking is a recent extension of traditional model-checking techniques for the integrated analysis of both qualitative and quantitative properties of systems which exhibit stochastic behaviour. In this paper we apply probabilistic model checking to study the effect of credit card companies on people's lives. We use the probabilistic model checking tool PRISM as the formal framework. This approach allows us to obtain performance measures on various policies. It allows us to obtain performance measures on various policies such as changes in the interest rate and its effect on the credit card loan entitlement of the card user, the effect of different repayment policies on the user’s spending ability in the short and long run, the effect of different interest rates and different spending preferences on the loan in the short run, and the effect of different spending preferences and different repayment policies on the remaining balance in the long run. From the study we investigate the level of loans and the amount of instalments after which the card holder goes through a cycle of interest repayment only. That is he/she can not use the card to withdraw money any more but has to make interest payments on the debt.