<![CDATA[Introduction/Main Objectives: The Average Effective Rate (TER) method was introduced to simplify tax calculation and provide greater certainty in the implementation of article 21 income tax. This study examines the effects of taxpayer perceptions, tax sanctions, and TRI NGA principles on the implementation of article 21 income tax using the TER method. Research Methods: This study employed a quantitative approach using a questionnaire to collect data form taxpayers in the Special Region of Yogyakarta, Indonesia. The data were analyzed using multiple linear regression with IBM SPSS version 27. Finding/Results: Specifically, the study found that taxpayers' perceptions have a positive effect on this application. Meanwhile, tax penalties do not influence the implementation of Income Tax Article 21 using the TER method, suggesting that the existence of penalties does not directly affect the application of this method. Furthermore, the Tri Nga teachings, which encompass the values of NGERTI (understanding), NGRASA (feeling), and NGELAKONI (practicing), have a positive influence on the implementation of Income Tax Article 21 using the TER method. Conclusion: These findings suggest that taxpayer perceptions and the internalization od TRI NGA principles are important factors in supporting the effective implementation of the TER method, whereas tax sanctions have not yet demonstrated a deterrent effect. The culture context of TRI NGA provides an important contextual dimension for understanding tax behavior in the Special Region of Yogyakarta. Future research may examine the applicability of TRI NGA or comparable cultural values in different regional contexts to strengthen the generalizability of the findings.]]>
