Think about a family of four earning $42,000 in 2016, which is between 150% and 200% of the federal poverty level. CBO says a mid-level “silver” plan will cost about $14,700 in premiums, of which the family will pay $2,600—since the government would pay the other $12,100. If the family breadwinner (or breadwinners, because the subsidies are based on combined gross income) then gets a raise or works overtime and wages rise to $54,000, the subsidy drops to $9,900. That amounts to an implicit 34% tax on each additional dollar of income.

Or consider a single worker earning $20,600 and buying an individual “silver” policy with a premium at $5,000. Again according to CBO, if his income rises to $26,500, his subsidy plummets to $2,700 from $4,400 (including a cost-sharing subsidy that goes away). This is a 29% marginal tax; moving to other income levels yields increases in the neighborhood of 20% to 23% for both individuals and families. Jim Capretta, a fellow at the Ethics and Public Policy Center, calculates that when combined with other policies like the Earned Income Tax Credit that also phase out, the effective marginal rate would rise to nearly 70% at twice the poverty level.

The incentives for low-wage workers are especially perverse. The exchanges give them a huge break and then take it away gradually as their income goes up. Usually such phase-outs are used to make sure “the rich” don’t benefit from IRS dispensations, but here they will have a giant effect on decisions about whether and how much to work, since each additional hour worked reduces the subsidy.