Mr. Trump and his top advisers have pitched the cut as a much-needed lift for consumers and businesses at a time when the spreading virus is beginning to chill economic activity. “The payroll tax holiday is probably the most important, powerful piece of this,” Larry Kudlow, the director of the National Economic Council, told reporters on Tuesday.

Under Mr. Trump’s plan — as described by Peter Navarro, one of his economic advisers — the government would, through the end of the year, stop collecting the 6.2 percent Social Security tax currently taken out of workers’ paychecks and the 1.45 percent tax taken for Medicare. It would also suspend equally large taxes paid on behalf of workers by their employers. Self-employed workers would be relieved of the entire 15.3 percent tax they currently pay.

For workers, earnings that are no longer subject to the payroll tax would now be subject to federal income taxes. Because lower-paid workers have lower marginal income tax rates, they would see a slightly larger percentage increase in their pay than workers with higher salaries. Some extremely high-paid workers would not see an increase at all because payroll taxes are capped by income, and some workers are close to — or have already reached — that limit. This means they are not set to have any Social Security taxes taken out for the rest of the year.

As a general rule, the largest percentage income gains would go to households earning up to $250,000 a year, according to calculations by the Tax Foundation, a nonprofit in Washington. The largest gains in dollar figures would go to households earning more than $123,000 a year, according to an analysis by the Institute on Taxation and Economic Policy in Washington.

How much individual workers would save depends partly on their employers. If an employer’s half of payroll taxes was lifted, they would need to decide whether to pass those savings directly to workers in the form of higher pay. Some economists see both sides of that equation as beneficial at a time of slowing economic activity.