CBO is required to assume that congressional appropriations continue increasing only at the rate of inflation for the 10 year baseline. They also extend emergency supplemental at their “current” level plus inflation over the duration of the baseline. For tax legislation, they assume current law will govern–so if there are tax cuts that have sunsets (as the 2001 and 2003 tax cuts have), CBO is required to project revenues assuming the tax cuts expire as written in the legislation. They also project economic growth in a very conservative fashion–they do not try to anticipate major changes in the economy, either recessions or accelerations.
The Concord Coalition takes the CBO baseline and adjusts it to assume appropriations increase at the same rate as the economy (GDP growth). This increase is closer to the historical average rate of increase. We also assume that supplemental appropriations do not continue indefinitely. For recent appropriations for the wars in Iraq and Afghanistan, we include realistic estimates from CBO about how much will be spent under a scenario where troop levels slowly decrease to about one-third of their level at the time of the estimate. We assume that Medicare physician payment cuts (under the Sustainable Growth Rate (SGR) are postponed, as they have been for the last several years.