The public debate on taxation of domestic small and medium enterprises (SMEs) versus large and multinational enterprises (MNEs) is highly relevant nowadays. Using confidential tax return data instead of financial statement data, the results indicate that domestic SMEs face on average a 1.6 and 4.8 percentage-point higher effective tax burden compared to large domestic and large MNEs respectively. This suggests that tax incentives for SMEs are inadequate to compensate for the tax advantages of large and internationally operating companies. Furthermore, we show that the use of information built exclusively upon accounting data could bias the results.

Using confidential tax return data, we provide a unique research setting in which the Belgian notional interest deduction (NID) is replaced by the Allowance for Growth and Investment (AGI) as it is proposed by the European Commission. Our results show that the AGI would be a more viable option from a budgetary view. From a company view, however, introducing an AGI system would increase the probability of a higher effective tax rate (ETR). Especially large companies would be harmed as they would face a 7.6 percentage point higher probability of an ETR increase compared with SMEs. Furthermore, we find that there is a positive relationship between the equity ratio and the increased ETR, which is stronger for large firms compared to SMEs. This is in line with previous studies stating that large firms adjusted more aggressively to the NID by increasing their equity ratio more heavily than SMEs. However, large firms still face an ETR that is on average 10.4 percentage points lower compared with SMEs, indicating that the AGI is insufficient to undo the unequal level playing field between large and small companies. (JEL codes: H21, G32, H25, K34).