"They really couldn't be more different," said Leonard Burman, director of the Urban-Brookings Tax Policy Center, which conducted the studies, said in a press call with reporters.
The differences begin with the deficit effects: The center says Clinton's plan would decrease the deficit by $1.6 trillion over 10 years with substantial tax increases on the wealthy and companies. Trump's would boost the deficit by $6.2 trillion over a decade with major tax cuts for the wealthy and companies.
Burman called the plans "mirror images" of each other. The analyses can be seen here.
The center did not account for the effects of either's candidates spending proposals or the growth effects from tax changes, so-called dynamic scoring.
Burman said that its analyses, sent in advance to both campaigns before being released publicly, had already garnered complaints from Trump advisors because they failed to account for the dynamic growth effects of its plan. The Trump campaign says that its tax cuts, along with loosening regulations and cutting government spending, will dramatically increase growth from the current average of around 2 percent per year to 3.5 percent and mitigate if not eliminate the deficit effects from lower taxes.
Burman said the center had initially planned to release estimates on growth, but a bug in a new economic model made it unconfident in its results. He said those estimates would be released in the next several days.
But the report already suggests some skepticism on the claims of the Trump campaign. It says that Trump's "marginal tax rate cuts would boost incentives to work, save, and invest if interest rates do not change." And it adds: "Increased investment could raise labor productivity and US wages by increasing capital per worker."
But the report warns that the increased government borrowing from higher deficits would raise interest rates and that those increases could offset any gains in growth from lower taxes, especially if investors see that the deficit is not on a stable path.
Burman was also skeptical that Trump would be able to slash government spending as much as promised, given that Trump has said military and Social Security and Medicare were off limits. Overall, Burman said Trump's plan would be positive in the short term for growth but potentially negative over the longer term.
Highlighting the dichotomy between the two plans, the center says Clinton's plan would be short-term negative and longer-term positive.
"Clinton's proposals would decrease incentives to save and invest, but only for filers in the top decile,'' the report said. "The higher rates levied on individuals' dividends and capital gains would raise corporations' cost of capital. All of these provisions would discourage saving and investment, although the responsiveness of saving to taxes is a subject of considerable debate among economists."
But longer-term positive effects could come from infrastructure spending, if carefully targeted. Trump has also pledged to increase spending on highways and bridges.
The report is clear in the effects of the proposed tax law changes on individuals. Under Clinton's plan, the top quintile of earners would see a 2.8 percent decline in after-tax income, with the top 1 percent seeing a 10.6 percent decline. All other quintiles would see gains, with the largest going to the bottom quintile of 0.6 percent.
Under Trump's plan, all quintiles would see gains in after-tax income, with the largest going to the top quintile of 6.6 percent. The top 1 percent of earners would see gains of 13.5 percent. But the lower quintiles would see larger gains in each case than in Clinton's plan.
But Burman added that because of some specific changes in the Trump tax plan, some middle class taxpayers, particularly single-parent families, would see tax increases.