Tax revenue forecasting is an essential input in the budgetary process. The ability to project and forecast future tax collections is an important element in the identification of future budgetary gaps and in the planning of new tax measures that may be needed to meet these needs. In addition, taxes play a major role in financing of the country’s economic and social development. It is the purpose of this paper to develop, specify and estimate a forecasting model for internal taxes. In particular, this paper attempts to estimate a tax-forecasting model that has a higher level of disaggregation.