One measure of the tax burden imposed on households is their effective tax rate (ETR)the total taxes they pay measured as a percentage of their pretax income. ETRs vary across types of households because of differences in sources and levels of income and in how the tax system treats taxpayers in different situations. Each year the Congressional Budget Office estimates ETRs for individual and corporate income taxes, payroll taxes, and excise taxes for different types of households, as well as all households as a group.