The share of pre-tax income accruing to the top 1% of earners in the U.S. has more than doubled to about 20% in 2010 from less than 10% in the 1970s. At the same time, the average federal income tax rate on top earners has declined significantly. Given the large current and projected deficits, should the top 1% be taxed more? Because U.S. income concentration is now so high, the potential tax revenue at stake is large.
But will taxable incomes of the top 1% respond to a tax increase by declining so much that revenue rises very little or even drops? In other words, are we already near or beyond the peak of the famous Laffer Curve, the revenue-maximizing tax rate?
The Laffer Curve is used to illustrate the concept of taxable income "elasticity,"—i.e., that taxable income will change in response to a change in the rate of taxation. Top earners can, of course, move taxable income between years to subject them to lower tax rates, for example, by changing the timing of charitable donations and realized capital gains. And some can convert earned income into capital gains, and avoid higher taxes in other ways. But existing studies do not show much change in actual work being done.
According to our analysis of current tax rates and their elasticity, the revenue-maximizing top federal marginal income tax rate would be in or near the range of 50%-70% (taking into account that individuals face additional taxes from Medicare and state and local taxes). Thus we conclude that raising the top tax rate is very likely to result in revenue increases at least until we reach the 50% rate that held during the first Reagan administration, and possibly until the 70% rate of the 1970s. To reduce tax avoidance opportunities, tax rates on capital gains and dividends should increase along with the basic rate. Closing loopholes and stepping up enforcement would further limit tax avoidance and evasion.
But will raising top tax rates significantly lower economic growth? In the postwar U.S., higher top tax rates tend to go with higher economic growth—not lower. Indeed, according to the U.S. Department of Commerce's Bureau of Economic Analysis, GDP annual growth per capita (to adjust for population growth) averaged 1.68% between 1980 and 2010 when top tax rates were relatively low, while growth averaged 2.23% between 1950 and 1980 when top tax rates were at or above 70%.
Neither does international evidence support a case for lower growth from higher top taxes. There is no clear correlation between economic growth since the 1970s and top tax-rate cuts across Organization for Economic Cooperation and Development countries.
For example, from 1970 to 2010, real GDP annual growth per capita averaged 1.8% and 2.03% in the U.S. and the U.K., both of which dramatically lowered their top tax rates during that period, while it averaged 1.72% and 1.89% in France and Germany, which kept high top tax rates during the period. While in no way does this prove that higher top tax rates actually encourage growth, there is not good evidence from the aggregate data supporting the view that higher rates slow growth.
One cannot evaluate the ultimate growth effects of raising more revenue without identifying what is done with the revenue. If part of the revenue is used to reduce the federal debt, more of savings go into capital investment, enhancing growth. The fact that those paying higher taxes will reduce their savings somewhat does not fully offset this effect as some of their higher taxes would come out of consumption.
If some of the additional revenue is used for public investments with a high return, such as education, infrastructure and research, it raises growth further. The neglect of public investment over the last few decades suggests that the returns could be quite high.
Large losses in efficiency come when people are limited in their ability to finance good investment opportunities. Surveys show difficulty of borrowing as an issue for start-ups. And higher education is influenced by the finances of parents, and the earnings premium for higher education is very high. Access to investment financing is a much bigger issue for low earners than for high earners. By the time Bill Gates got rich, Microsoft was not likely to have trouble financing investments. Hence, increasing tax rates on the already rich might not hurt growth as much as increasing tax rates on the soon-to-be rich.
By itself, a suitable increase in the taxation of top earners will not solve our unsustainable long-term fiscal trajectory. But that is no reason not to use this tool to contribute to addressing this problem.
Mr. Diamond is professor emeritus at MIT and a Nobel laureate in economics. Mr. Saez is a professor of economics at UC Berkeley and a John Bates Clark medalist.