As discussed in yesterday’s blog post and in CBO’s The 2014 Long-Term Budget Outlook, if current laws remain generally unchanged, debt held by the public is projected to exceed its current percentage of GDP—74 percent—after 2020 and to continue rising on a path that would ultimately be unsustainable. To put the federal budget on a sustainable path for the long term, lawmakers would have to make significant changes to tax and spending policies: reducing spending for large benefit programs below the projected levels, letting revenues rise more than they would under current law, or adopting some combination of those approaches.
One way to think about the magnitude of that challenge is to assess the changes in spending or revenues that would be needed to achieve a chosen goal for federal debt.
What Are the Size of Policy Changes Needed to Meet Various Goals?
The size of such changes would depend on the amount of federal debt that lawmakers considered appropriate. For example, a combination of cuts in noninterest spending (that is, spending excluding interest payments) and increases in revenues that equaled 1.2 percent of GDP in each year beginning in 2015—about $225 billion in that year—would hold debt 25 years from now, in 2039, to the same percentage of GDP that it is now (without accounting for the economic effects of the reduction in debt or of the policy changes that might be used to achieve it), by CBO’s estimate. If those changes came entirely from revenues, they would amount to a roughly 6½ percent increase relative to the revenues projected for the 2015–2039 period under current law. If the changes came entirely from noninterest spending, they would represent a cut of 6 percent from the amount of noninterest spending projected for that period.
 Another option for lawmakers would be to set a goal of bringing debt held by the public back down to the average percentage of GDP seen over the past 40 years—39 percent. As shown in the figure below, meeting that goal by 2039 would require much larger changes in tax and spending policies—a combination of increases in revenues and cuts in noninterest spending, relative to current law, totaling 2.6 percent of GDP in each year beginning in 2015 (again, without accounting for the economic effects of the reduction in debt or of the policy changes that might be used to achieve it). In 2015, 2.6 percent of GDP would equal about $465 billion. If those changes came entirely from revenues, they would represent an increase of 14 percent from the revenues projected for the 2015–2039 period under current law. If the changes came entirely from noninterest spending, they would represent a cut of 13 percent from the amount of noninterest spending projected for that period.
