This document provides additional details on the Congressional Budget Office's (CBO) long-term projections for Social Security. It finds that Social Security tax revenues will be insufficient to cover scheduled benefits starting in 2020, resulting in the trust funds being exhausted by 2038. Under an alternative scenario with lower revenue and higher costs, the trust funds would be exhausted by 2023. The document also examines how benefits would be reduced if outlays had to be limited to tax revenues.