Former President Donald J. Trump has been offering up new tax cuts to nearly every group of voters that he meets in recent weeks, shaking the nerves of budget watchers and fiscal hawks who fear his expensive economic promises will explode the nation’s already bulging national debt.

But on Tuesday, Mr. Trump made clear that he was unfazed by such concerns and offered a one-word solution: growth. Despite the doubts of economists from across the political spectrum, Mr. Trump said that he would just juice the economy by the force of his will and scoffed at suggestions that his pledges to abolish taxes on overtime, tips and Social Security benefits could cost as much as $15 trillion.

“I was always very good at mathematics,” Mr. Trump told John Micklethwait, the editor in chief of Bloomberg News, in an interview at the Economic Club of Chicago.

Faced with repeated questioning about how he could possibly grow the economy enough to pay for those tax cuts, Mr. Trump dismissed criticism of his ideas as misguided. He professed his love of tariffs and insisted that surging output would cover the cost of his plans.

“We’re all about growth,” Mr. Trump said, adding that his mix of tax cuts and tariffs would force companies to invest in manufacturing in the United States.

The national debt is approaching $36 trillion. The Committee for a Responsible Federal Budget projected last week that Mr. Trump’s economic agenda could cost as much as $15 trillion over a decade. Economists from the Peterson Institute for International Economics, a nonpartisan think tank, estimated last month that if Mr. Trump’s plans were enacted, the gross domestic product could be 9.7 percent lower than current forecasts, shrinking output and dampening consumer demand.

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