It is easy to look at charts like the one above and dismiss the FairTax as simply another way to help the rich get richer. But there is an economic argument for a less progressive tax system, though that argument is extremely technical. Kotlikoff has asserted that the FairTax will lower the marginal tax rate for all earners. (The marginal rate is the tax rate paid on the last dollar earned.) Because marginal rates are lower, each extra dollar of income will result in greater purchasing power. The decrease in marginal rates is progressive – that is, marginal rate reductions are greater for the working- and middle-classes than for the wealthy.

Moreover, even FairTax critics like Gale agree that consumption taxes increase the size of the economy. Many studies show that long-term incomes would rise under a consumption-based tax system. Optimistic accounts show a 10 percent rise in income over time, but even the more cautious studies show gains of 5 percent to 7 percent. Because the FairTax will grow the economy, workers will eventually see increases in their income. FairTax proponents claim that the growing economy, coupled with the reduction in marginal tax rates, will offset the increased tax burden. Burton argues that "the FairTax is a positive-sum game," one in which purchasing power will grow faster than the tax burden.

Economist William G. Gale at the Brookings Institution writes: "Under the AFT proposal, taxes would rise for households in the bottom 90% of the income distribution, while households in the top 1% would receive an average tax cut of over $75,000." Gale continues, "If households are classified by consumption level, a somewhat different pattern emerges. Households in the bottom two-thirds of the distribution would pay less than currently, households in the top third would pay more."[24] While Gale's analysis differed from the FairTax legislation,[22] he is referring to absolute tax money—ranked by income, households at the lower end of the distribution will tend to pay more in absolute taxes, while households at the higher end will tend to pay less in absolute taxes. Ranked by spending or consumption, households that currently spend less on consumption would pay less total taxes, while households that currently spend more would pay more. For example, a family of four (a couple with two children) earning about $25,000 and spending this on taxable goods and services, would consume 100% of their income. A higher income family of four making about $100,000, spending $75,000, and saving $25,000, would consume only 75% of their income on taxable goods and services. When presented with an estimated effective tax rate, the low-income family above would pay a tax rate of 0% on the 100% of consumption and the higher income family would pay a tax rate of 15% on the 75% of consumption (with the other 25% taxed at a later point in time). A person spending at the poverty level would have an effective tax rate of 0%, whereas someone spending at four times the poverty level would have an effective tax rate of 17.2%.[25]

These conclusions are contradictory according to Gale. The FairTax proposal is regressive on income (using a cross-section time frame) and progressive on sales.[22]