Donald Trump's tax reform plan would amount to either a $4.4 trillion or a $5.9 trillion tax cut, according to a new outside analysis, depending on whether a small business tax cut is included in the plan. The Trump campaign hasn't made clear whether that provision is included.

The Tax Foundation, a nonprofit think tank, found that Trump's plan would also spur economic growth by reducing tax rates and boosting the rewards for investing and saving. As a result, in a "dynamic analysis" that takes into account the revenues from that economic growth, Trump's plan would cost the Treasury less: Either $2.6 trillion or $3.9 trillion, depending on whether the small business tax cut is included.

The analysis released Monday partially represents a success for the Republican presidential candidate. His team had sought to revise his plan after earlier scores indicated that it would cut too deeply into federal revenues. An earlier analysis from the Tax Foundation found that the Trump plan would reduce revenues by almost $12 trillion, or about a quarter of federal revenues over 10 years.

But the new analysis will also bring new scrutiny to the Trump campaign's ambiguous statements about the small-business tax rate, which accounts for about $1.5 trillion in the analysis, a major question mark.

It also shows that the tax plan is still regressive because it would make the tax code less progressive in terms of income distribution. Depending on whether the small-business cut is included, after-tax incomes for the top 1 percent would rise by 10 percent or 16 percent. Middle- and lower-class incomes, however, would only rise by 1 percent to 2 percent.