This article presents a short-term interest rate monetary model; it generalises Junca and Rodriguez's interest rate formation model and captures the exogenous and endogenous factors determining monetary supply and short-term interest rate behaviour. Short-term interest rate rises with increased expectations of future inflation, external interest rate and future short-term interest-rate expectations. The model shows that a policy for controlling the amount of money could stabilise the short-term rate, as well as other interest rates.