Mr. Sanders’s plan would eliminate health insurance premiums and almost all out-of-pocket costs. But he would compensate by raising taxes, and his financing ideas include a payroll tax that would affect many middle-class Americans. Assessing the overall effects on individual Americans is not possible under his plan, because he has not been specific about the particular tax increases he would use.

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“For virtually everybody,” Mr. Sanders said at last week’s debate, “the tax increase they pay will be substantially less — substantially less than what they were paying for premiums and out-of-pocket expenses.”

Ms. Warren has sought to reframe the question of raising taxes around the total costs that families would face under Medicare for all. She has said that costs would go up for wealthy people and big corporations, but would go down for middle-class families.

“I will not sign a bill into law that does not lower costs for middle-class families,” Ms. Warren said at the debate, a pledge she repeated in Iowa on Sunday.

The campaign of one of Ms. Warren’s top rivals, former Vice President Joseph R. Biden Jr., noted on Sunday that Ms. Warren committed to releasing a financing plan only after being pushed on the issue.

“It’s mystifying that for someone who has put having a plan for everything at the center of her pitch to voters, Senator Warren has decided to release a health care plan only after enduring immense public pressure for refusing to do so,” a spokesman for the Biden campaign, T.J. Ducklo, said. He added that the Biden campaign hoped Ms. Warren’s plan “will be straight with the American people about how much middle-class taxes will go up.”