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1/2026 vol. 325
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RESEARCH PAPER
Estimation of the Personal Income Tax (PIT) Gap in Poland
Tomasz Tratkiewicz 1
,
 
Mehmet Burak Turgut 2
 
 
 
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1
Institute of Finance, University of Lodz, Poland
 
2
Department of Macroeconomics and Foreign Trade Theory, University of Warsaw, Poland
 
 
Submission date: 2024-12-26
 
 
Final revision date: 2025-05-19
 
 
Acceptance date: 2025-06-05
 
 
Publication date: 2026-03-31
 
 
Corresponding author
Tomasz Tratkiewicz   

Institute of Finance, University of Lodz, Poland
 
 
GNPJE 2026;325(1):5-22
DOI: https://doi.org/10.33119/GN/214918
 
 
Article (PDF)
References (46)
 
KEYWORDS
personal income tax
tax gap
risk-based audit
sample selection model
 
JEL CLASSIFICATION CODES
ABSTRACT
The literature on estimating the tax gap in direct taxes generally emphasises that using a bottom-up method produces much better results than using a top-down method. The existing methods of estimating the PIT gap using the bottom-up approach rarely take advantage of risk-based audits, which can be successfully used when tax gap estimation based on random audits cannot be applied. An important issue with risk-based audits is the potential selection bias. To address this issue, we use the Heckman selection model. We estimate the size of the PIT gap in Poland in 2017 by using data from the tax filings of taxpayers earning income from business activities taxed at a flat 19‑percent tax rate and risk-based audits. Our findings show that the predicted PIT gap corresponds to 4.5 percent of the total tax liability of this group of taxpayers. We also identify the regions and sectors with the highest predicted PIT gap per taxpayer. Our results show that the Heckman model can be used as a tool by tax authorities to improve the efficiency of risk-based audits.
ACKNOWLEDGEMENTS
We would like to thank three anonymous referees for helpful comments, Centrum Projektów Europejskich for financial support (Project. No. POWR.04.03.00-00-0047/17) and CASE – Center for Social and Economic Research for making the research possible. We are solely responsible for the interpretation of the data and all errors.
FUNDING
Centrum Projektów Europejskich (Project. No. POWR.04.03.00-00-0047/17)
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