Another large, though less-noticed, tax cut in Mr. Trump’s plan is a reduction in the maximum tax rate on “pass-through income” to 15 percent; currently, this income is taxed at the same rates as wage income, up to 39.6 percent.

Pass-through income is often described as “small-business income,” but that term can be misleading. Small-business owners can use corporate structures, like limited liability companies, that are not taxed. Instead, the income from these companies is passed through to their individual owners, who then pay tax on their individual income tax returns. Those small-business owners would enjoy this tax reduction from Mr. Trump, but so would the owners of large businesses that may also choose to use these same ownership structures. The tax break would also go to independent contractors like me: The New York Times pays me a salary, but when I do work for other organizations, I treat the payments as small-business income, and I’d get to use the 15 percent rate proposed by Mr. Trump.

In addition to offering huge tax cuts to the rich and to business owners (including me!), Mr. Trump would offer huge tax cuts for the middle and upper-middle class. Married couples would pay no tax on their first $50,000 of income and just 10 percent on the next $50,000. A married couple with no children earning $100,000 and taking the standard deduction would pay $11,437 in income tax under today’s rules; under Mr. Trump’s plan, they would pay just $5,000, a tax cut of 56 percent. Many people with low-to-moderate incomes would see their income tax bills reduced to zero, increasing the share of the population that pays no income tax at all.

He’d also offer huge tax breaks to corporations, which would pay 15 percent, down from a current rate of 35 percent. Corporate tax is the main place where his plan departs from Republican orthodoxy, but in a fairly arcane way. Mr. Trump would tax the worldwide income of American corporations at the time it is earned. Currently, American companies may delay tax on foreign profits until they return those profits to the United States. Many Republicans (including Jeb Bush) would move in the other direction and forgo tax on foreign income altogether, arguing that worldwide taxation makes it harder for American companies to compete abroad.

By demanding immediate tax on foreign profits, Mr. Trump’s plan would disfavor American companies that locate their businesses abroad, which is consistent with his broader theme of pushing companies to return factories and jobs to the United States. However, because he would cut the corporate income tax rate so steeply, the effects of immediate worldwide corporate taxation would be limited: Companies get a credit for tax paid to other countries, so Mr. Trump’s tax would apply only on foreign profits that were not subject to tax by a foreign country at a rate of at least 15 percent. This would mostly affect income earned in tax havens, as most major countries have corporate income tax rates of more than 15 percent.

In other words, Mr. Trump’s worldwide tax plan would have no effect on Ford’s choice to make cars in Mexico, so long as they’re paying at least 15 percent in tax to Mexico on their Mexican activities.

A document from the Trump campaign says all these tax cuts would be “fully paid for” by the elimination of deductions and by a one-time tax on foreign profits of American firms held abroad. That math simply does not add up: As discussed above, rich people do not currently take enough tax deductions to offset the tax rate cuts Mr. Trump proposes, and the one-time foreign profits tax might raise $250 billion, not close to the trillions of revenue that would be lost through tax rate cuts.

At a news conference Monday, Mr. Trump offered another way his tax plan would pay for itself: economic growth, perhaps as fast as 6 percent a year, again a higher-energy estimate than the 4 percent Mr. Bush has proposed. But there is no evidence to support the idea that such rapid growth can be produced through tax cuts.