This paper discusses the estimates of tax gaps for corporate income tax (CIT) for nonfinancial corporations in Slovenia by applying the methodology of the IMF’s Revenue Administration – Gap Analysis Program (RA-GAP). The RA-GAP methodology for CIT gap is based on a top-down approach, which estimates the potential tax base and liability from macroeconomic data. The top-down estimation of the CIT gap provides an initial evaluation of the level and change in taxpayers’ compliance; however, further work in some areas is needed to improve the application of the methodology and reliability of results. Assessed CIT for nonfinancial corporations dropped from 2011 to 2012 then rose until 2020; potential CIT roughly followed the same pattern. The estimates for the assessment gap for nonfinancial corporations indicate there may have been an increase in 2012, and then a decline back to the 2011 levels. Under either method, the bulk of the assessment gap appears to be in the manufacturing sector.