This study aims to analyze the evolution of tax management in companies listed on Euronext Lisbon from 2017 to 2021 and to compare data on the national average effective tax rate (ETR) with the average ETR of the companies in the sample. The data was collected in the SABI database and manually through content analysis of the companies’ financial statements. A quantitative methodology was adopted in data processing, and an ETR variable was constructed to measure tax management: the lower the ETR, the greater the tax management. The results reveal significant variations in ETR values among companies and within observations about the same company. On average, and in the period under analysis, listed companies in the sample support an ETR of around 30%, much higher than the average ETR for all Portuguese companies (around 21%). This disparity may be due to the state surcharge for taxable incomes exceeding 1.5 million euros. However, some observations present very low ETR values; in some cases, they are close to zero. There is heterogeneity in the sample since there is one observation with an ETR of 0.3% and another with an ETR of 174.6%. Society perceives that listed companies pay less taxes in relative terms; that is, they have, on average, a lower ETR than other companies. Thus, the results of this study make significant contributions to society and the business world (shareholders, managers, auditors, accountants, and consultants), as well as to regulators/legislators who deal with tax issues.