Implicit marginal tax rates, again

Greg Mankiw writes in the Times and discusses:

A family of four with an income, say, of $54,000 would pay $9,900 for health care. That covers only about half the actual cost. Uncle Sam would pick up the rest.

Now suppose that the same family earns an additional $12,000 by, for example, having the primary earner work overtime or sending a secondary worker into the labor force. In that case, the federal subsidy shrinks, so the family’s cost of health care rises to $12,700.

In other words, $2,800 of the $12,000 of extra income, or 23 percent, would be effectively taxed away by the government’s new health care system.

That implicit marginal tax rate of 23 percent is a significant disincentive. And it comes on top of the explicit marginal tax rate the family already faces from income and payroll taxes. Altogether, many families would face marginal rates at or above the 50 percent level that animated the Reagan supply-side revolution.

[..] there is no simple fix. Higher marginal tax rates are an integral part of the Obama health plan.