After long resisting that idea, the budget office recently signaled that it agrees, and it plans to lower its estimates next year. But for now, Republicans have seized on the unadjusted estimates, because fewer people with government-subsidized insurance means more money to help them finance other parts of their tax overhaul bill.

It looks as if the tax bill rises for some people who drop coverage.

Here’s why: The subsidies Obamacare offers to low- and middle-income Americans who buy their own insurance take the form of refundable tax credits, a kind of government-issued gift card that can be used only to buy health insurance. But if fewer people who qualify for these gift cards choose to buy insurance, the government spends less in tax money for the population that qualifies. The tax scorekeepers count this reduction in tax credits as an increase in tax liability for the group. Individuals would not actually pay more in taxes.

If they don’t buy insurance and don’t get the gift card, is that really the same thing as paying more in taxes? Republicans say it is not.

“Nothing in our mark will impact the availability of premium subsidy credits,” said Senator Orrin Hatch of Utah, the chairman of the Senate Finance Committee, on Thursday, using a technical term for draft legislation. “This is the result of an assumption about economic behavior that is 100 percent voluntary.”

Mr. Hatch has a point. The subsidies may count, technically, as tax benefits, but they are relatively unusual in the tax code, because they can be used only to buy health insurance. People who get insurance can get a gift card. People who don’t get nothing. But if someone chooses not to buy insurance, does that mean they’ve lost out financially?