To arrive at $440 billion, IBD argues that the tax plan cut tax revenue by $1.69 trillion but caused GDP growth producing $1.1 trillion in new revenue. However,

To arrive at $440 billion, IBD argues that the tax plan cut tax revenue by $1.69 trillion but caused GDP growth producing $1.1 trillion in new revenue. However, the $1.69 trillion figure already factored in GDP growth, so they double counted.[1] I'm surprised that they made such a basic mistake. You should read less IBD and more NYT. [1] CBO Appendix A, page 93: "Legislative changes... led CBO to increase its projection of the cumulative deficit over the 2018–2027 period by $2.7 trillion. Those changes were offset in part by the effects of revisions to CBO’s economic forecast, which led to $1.0 trillion in reductions to projected deficits, almost entirely because of increased projections of revenues."