The Joint Committee on Taxation (“JCT”) released their dynamic score of the Senate Bill as reported by the Senate Finance Committee this afternoon. You can read the release here.

The JCT estimates that the Senate Bill would increase the level of GDP relative to the baseline forecast by 0.8 percent on average throughout the ten-year budget window.   This forecasted increase in GDP reduced the JCT’s estimates of the revenue lost by the Senate Bill over the 10-year budget window by $458 billion over the JCT’s static score, resulting in an estimated revenue loss of $956 billion over the budget window.

Much of the debate this afternoon on the Senate Floor concerned the accuracy of the JCT’s estimates of the economic growth that would be caused by the Senate Bill, with Republican members of Congress asserting that the JCT’s dynamic score significantly underestimates the level of economic growth that would be produced by the Senate Bill.

The baseline forecast used by the JCT was published by the Congressional Budget Office in January 2017, and was prepared using “current law” assumptions.  In other words, it assumed that current tax provisions that are scheduled to expire over the 10-year budget horizon will expire as scheduled.  Republican leadership has long argued for the use of a “current policy” baseline that takes into account Congress’s history of extending such provisions before expiration, arguing that “the current law baseline is not the proper standard for determining whether tax reform is revenue neutral.” We wrote about the differences between “current law” and “current policy” baselines here.