The marginal tax rate is the rate on the last dollar of income earned. This is very different from the average tax rate, which is the total tax paid as a percentage of total income earned. In 2003, for example, the United States imposed a 35 percent tax on every dollar of taxable income above $155,975 earned by a married taxpayer filing separately. But that tax bracket applied only to earnings above that $155,975 threshold; income below that cutoff point would still be taxed at rates of 10 percent on the first $7,000, 15 percent on the next $14,400, and so on. Depending on deductions, a taxpayer might pay a relatively modest average tax on total earnings, yet nonetheless face a 28-35 percent marginal tax on any activities that could push income higher--such as extra effort, education, entrepreneurship, or investment. Marginal decisions (such as extra effort or investment) depend mainly on marginal incentives (extra income, after taxes).... MORE