Meanwhile, experts are trying to figure out where the extra revenue came from. Leonard Burman, a former Treasury official and now an economist at the Urban Institute, suspects the April-May revenue jump reflects a surge in nonwithheld personal taxes - big bonuses, for instance, paid by Wall Street firms to their executives and other top employees, or handsome capital gains from stock sales in the resurgent stock markets.
Another factor: The well-to-do have been getting richer, and they still face higher tax rates than average taxpayers or the poor, despite the Bush tax cuts.
Thanks to a rise in corporate profits last year, corporate tax payments have also risen 47 percent. Moreover, a special tax break, a bonus depreciation on investments in plant and equipment, expired at the end of 2004.