PurposeThe present study aims at quantifying the likely impacts of an environmental tax on macroeconomic variables and pollution in Iran.Design/methodology/approachThe computable general equilibrium model, which allows the prediction of the economy-wide effects of any change in policy instruments, is applied.FindingsThe main findings reveal that gross domestic product, private consumption and income in both urban and rural areas will follow a declining trend as a result of environmental tax imposition. In a scenario with the highest level of tax, the predicted percentage change to the gross domestic product and private consumption is estimated at −21.32 and −40.96, respectively. In the same scenario, pollution emissions would decrease by 12.4–22.6% for CO2, CH4 and N2O.Originality/valueThis study uses a general equilibrium model to examine the effects of the carbon tax on environmental issues and household welfare, considering the unique conditions and regulations of Iran. While the related literature examines the CO2 tax, the current study covers more pollutants, including CO2, CH4, N2O, CO, SO2 and NOx. In addition, a distinguishing feature of the current study is that it applies a modified version of the social accounting matrix (SAM) database, which includes the heavy subsidies of energy products. Another significant feature of the current study is that it examines tax policy while tax rates are exerted endogenously (compared to previous studies).