The Real Property Mass Valuation Act (ZMVN), adopted in 2006, was followed by Real Property Mass Valuation Act (ZMVN-1), adopted in 2017. The new law has changed the methodology according to which houses are valued. With the new law, different input data are taken into account, the method of calculating real property value is different, and above all, the methodology has been simplified. The necessary data for the calculations were obtained from website of the Surveying and Mapping Authority of the Republic of Slovenia. The calculations of the value of the houses are explained step by step, with a description, equations and a graphic display. In the master's thesis, we analyze changes in the methodology of calculating the generalised value of real property or houses and present the importance of correct data in surveying records. The master's thesis is divided into several chapters, starting with introducing the theory of mass valuation of real property, its development and use in Slovenia. Both valuation acts are defined on the basis of which the mass valuation of real property in Slovenia has been implemented. We also present other models of real property valuation, data we need and a more detailed description of the valuation model for houses. The core of the master's thesis is the chapter on the methodological approach with a description of the area of work, types of real property and data collected. In the concluding chapters, the results of the analytical part are presented with a graphic display and critical discussion, followed by the presentation of the main findings of the research and conclusion.