So I've been thinking a lot about how the Joint Committee on Taxation projects its excise tax revenue, and the more I think about it, the more I realize just how much of the revenue they're projecting comes from a pretty elaborate dynamic effect on the labor market.
I got some clarity from sources in the know about how the CBO calculated that somewhat cryptic "Other Effects on Tax Revenues and Outlays" that generates $83 billion to defray the costs of the program over ten years. Basically, the CBO's assumption is that the attractiveness of the subsidies will encourage several million people to drop their employer insurance and buy subsidized insurance on the exchange. Their employers will pay them more money instead, and this money will be taxed.
Similarly, the Joint Committee on Taxation, which calculated the revenue from the excise tax, assumed that almost three quarters of the benefit would come from employers driving down their insurance costs, passing on the savings to their workers as compensation, and that compensation getting taxed. And because the pressure to cut costs is expected to gather steam over time, the effect is larger in the out years--by 2019, the JCT predicts $46.3 billlion worth of revenue, but only $7.9 billion of it comes from people actually paying the tax. The rest is dynamic effects.