Former CBO director Rudy Penner, a senior Fellow at the Urban Institute, examines how much economic would reduce the burden of rising entitlement costs. The money paragraph on Social Security:
A 0.5 percent increase in the annual rate of productivity growth reduces the 75-year actuarial deficit from 1.95 percent of payroll to 1.39 percent (or by 0.56 percent of payroll). Roughly speaking, it would be necessary to double today’s 1.9 percent assumed rate of productivity growth to solve Social Security’s long-run actuarial problem with economic growth. Although there have been short periods of such high productivity growth over the past five decades, it is totally implausible to believe that such growth could last over 75 years.The full text is available here.