The article deals with the VAT gap, its split by causes and determinants, the problem of dependencies. The article also reveals the main ways of calculating the VAT gap - their advantages and disadvantages, summarizes the research done by theoreticians and evaluates the research results. After the theoretical analysis and presentation of the research methodology, the aim is to find out the variables that influence the VAT gap in Lithuania. Using the regression analysis model, the factors determining the VAT gap and their significance, as well as their impact on the decrease / increase of the VAT gap in Lithuania, were identified.