would be as follows for a single taxpayer with no dependents in 2006: This would appear to be highly progressive - the person with the higher taxable income pays tax at twice the rate. However, if you divide the tax by the amount of gross income (i.e., before deductions), the effective rates are 11% and 23%: the higher income person's rate is still twice as high, but his deductions drive down the effective rate more quickly ((14%-11%)/14% = a 21.4% effective tax rate savings or discount at the low income bracket; (31%-23%)/31% = a 29% effective tax rate savings or discount at the higher income tax bracket). To make the two tax rates realize an equal savings or discount from taking the maximum allowable deductions, the higher income tax bracket would have to have an effective tax rate of ~24.35% (31%-24.35%/31% = 21.4% or the same discount as the lower tax bracket) instead of 23%. This would necessitate an additional income tax of $1,975 from the higher tax bracket ($200,000*24.35% [new and equal effective tax rate] = $48,700), or an extra 0.99% in this model. FICA taxes Discussions of income tax progressivity often do not factor the payroll taxes (FICA - social security and medicare taxes), which have a "ceiling". This is because these insurance benefits are directly determined by individual contributions over that individual's lifetime. Thus, since payroll taxes serve as direct individual premiums for direct individual benefits, most do not include these taxes in the calculation of the progressive nature of federal taxes, just as they do not include similar private automobile, homeowners, and life insurance policy premiums. Another factor is that the social benefits themselves are paid in a progressive nature; individuals with lower lifetime average wages receive a larger benefit (as a percentage of their lifetime average wage income) than do individuals with higher lifetime average wages. However, if one were to expand the tax distribution example to include social security insurance taxes: Some lower income individuals pay a proportionately higher share of payroll taxes for Social Security and Medicare than do some higher income individuals in terms of the effective tax rate. All income earned up to a point, adjusted annually for inflation ($106,800 for the year 2010) is taxed at 7.65% (consisting of the 6.2% Social Security tax and the 1.45% Medicare tax) on the employee with an additional 7.65% in tax incurred by