One aspect of the new Trump tax plan that got some attention from journalists, because it was confusing, was its treatment of business taxation. The Trump campaign told the National Federation of Independent Business that the plan included a big tax cut for businesses that pay the individual income tax rather than the corporate income tax, and the NFIB endorsed Trump. It told the Tax Foundation otherwise, which would lower the group’s estimate of the plan’s impact on the deficit. The Foundation ended up doing two estimates of the plan’s effects, one with the tax cut for noncorporate businesses and one without it. The smaller version of the tax cut would leave a revenue hole of $4.4 trillion over ten years, the bigger version a $5.9 trillion one. The government could try to make up that hole by cutting spending or hoping the plan generates a lot of extra economic growth; or it could just let the debt grow.

Both sets of estimates, though, are probably too low because of another big ambiguity in the plan. One way to read the plan is that a family with a stay-at-home mom will get a tax deduction equal to the average cost of child care in the state. That’s the way I read it last week, and it’s a reading supported by a comment Trump made in a speech. Ryan Ellis did a back-of-the-envelope estimate of the revenue impact of the child-care deduction that incorporated that assumption, and it came to $1.8 trillion over ten years. But the Tax Foundation assumed that stay-at-home moms would get a smaller deduction than that, and their estimate was only $500 billion. We may have to get much closer to the passage of Trump’s plan to find out what’s in it.