As part of its activities, focused on analyzing and checking the Government's macroeconomic and public finance forecasts, the Parliamentary Budget Office (PBO) has launched a programme to develop tools for monitoring and forecasting public finances and for assessing the effects of the most important legislative measures. Part of this activity is the development of a model for analyzing and forecasting the expenditure for interest on domestic government securities1, which enables the impact of changes in interest rates on interest expenditure to be assessed in the short and medium term and the debt management policy to be analysed (historical analysis).