In 2007 Slovenia launched a comprehensive reform of its tax system. To estimate the different proposals (including a flat-tax proposal) and their overall effect on individual taxpayers and government budget a static micro-simulation model was constructed and combined with a computable general equilibrium model. It uses a large, comprehensive database (6% of the population) provided by relevant ministries and government agencies and proved to be a reliable tool during implementation of the reform. In the paper, the main characteristics of both models are presented along with the results of different reform scenarios, including those which finally passed the parliament and now form part of the Slovenian tax system.