This paper presents a methodological framework for the development of a multiregional economic forecasting and simulation model for Spain’s 19 Autonomous Communities and Cities over the medium and long term. Within a context of increasing decentralization and the pressing need for homogeneous statistical data, there is a notable lack of consistent regional data from an aggregate demand perspective. To address this limitation, an annual regional database (1995–2023) was constructed, comprising 40 variables per region. This dataset includes domestic and external demand components—in both nominal and volume terms—as well as labor market indicators.

The model employs a hybrid “bottom-up” and “top-down” approach, implemented in EViews, and is grounded in structural econometric models with error correction mechanisms (ECM). Each region is represented by an independent model that is subsequently reconciled with a national framework. The methodology incorporates region-specific prices, interregional interactions, and exogenous national and international variables. Furthermore, the model facilitates the generation of simulations and alternative scenarios, proving instrumental in evaluating policies such as the implementation of European funds or the impact of tariff fluctuations. Currently, the model generates projections through 2050, providing a robust tool for regional economic planning.