WASHINGTON — When people heard that Mitt Romney’s federal income tax rate was about 15 percent, the immediate reaction of many was to assume that their own rate was higher. The top marginal rate is 35 percent, after all, and the marginal rate on a couple with $70,000 in taxable income is 25 percent.

The truth is that most households probably pay a lower rate than Mr. Romney. It is impossible to know for sure, given that he has yet to release his tax return. What is clear, though, is that a large majority of American households — about two out of three — pays less than 15 percent of income to the federal government, through either income taxes or payroll taxes.

This disconnect between what we pay and what we think we pay is nothing less than one of the country’s biggest economic problems.

Many Americans see themselves as struggling under the weight of a heavy tax burden (partly for the understandable reason that wage growth has been so weak). Yet taxes in the United States are quite low today, compared with past years or those in other countries. Most important, American taxes are not sufficient to pay for the programs that many people want, like Medicare, Social Security, road construction and education subsidies.