[U[nder CBO's base-case scenario ― called the "extended baseline scenario" ― annual budget deficits never fall below 3 percent of GDP after 2019 and federal debt held by the public (which excludes federal debt held by federal trust funds) would reach 100 percent of GDP by 2038.
CBO expects that 54 percent of the federal spending increase on the major entitlements over the next twenty-five years will be attributable to the aging of the U.S. population. Twenty-eight percent of the increase will be due to “excess cost growth” in health care ― meaning cost escalation per capita in excess of GDP growth per capita. The rest of the spending increase is due to the expansion of Medicaid and the new premium credits enacted in the PPACA. When looking at just the health care entitlements, 40 percent of the federal spending increase is due to excess cost growth, 35 percent from population aging, and 26 percent from the PPACA program expansions.