The Social Security Advisory Board’s Technical Panel concluded that the Social Security Trustees’ “assumptions and methodologies are basically sound.” But these “basically sound” assumptions understate Social Security’s projected 75 year shortfall by $2.6 trillion compared to the technical panel’s recommended assumptions.

According to the trustees, Social Security’s 75 year shortfall amounts to 2.68 percent of taxable payroll, or $9.4 trillion, over the next 75 years. But according to the technical panel tasked with evaluating the trustees assumptions, Social Security’s shortfall is 3.42 percent—a 28 percent, or roughly $2.6 trillion difference.

While the panel’s chair, Alicia Munnell, implied that a 0.74 percent difference in taxable payroll is no big deal, that’s an extra $22,000 in lifetime Social Security taxes for an average worker making $50,000 per year.

So how do the trustees’ assumptions lead to lower shortfalls?

  1. Higher fertility rates: Fertility rates matter because the more babies that are born, the more future workers there are paying into Social Security. The fertility rate has been declining in the U.S., and currently stands at 1.86. However, the trustees assume a 2.0 fertility rate while the Panel recommends a rate of 1.9.
  1. Lower mortality improvement rates: The longer individuals live, the longer they collect Social Security benefits. By assuming low mortality improvement rates, the trustees’ project retirees will collect fewer benefits. Despite six successive panels concluding that the trustees’ mortality improvement assumptions are too low and lack convincing rationale, the trustees’ have not adjusted their assumptions. The panel’s recommended mortality adjustments would increase the trustees’ assumptions for life expectancy at birth in 2090 by 2.4 years (to 88.3) and at age 65 by 1.7 years (to 90.3).
  1. Higher Interest Rates: Interest rates affect the amount of income credited to the Social Security trust fund as well as the computation of future cash-flows that project the system’s overall finances. The trustees’ projected interest rates exceed those of other organizations and forecasters. The Panel recommends that the trustees lower their real interest rate assumptions from 2.9 percent to 2.5 percent and their nominal rate from 5.6 percent to 5.0 percent.

While fertility, mortality and interest rates accounted for nearly all of the difference in projected shortfalls, the panel also recommended the trustees raise their assumption for net immigration, reduce their disability insurance recovery rate, reduce their assumed share of taxable earnings, and lower their inflation assumptions.

Even under the trustees’ arguably generous assumptions, Social Security will come up $9.4 trillion short over the next 75 years ($12.2 trillion counting all the IOUs in the trust funds). Commonsense reforms could preserve Social Security’s retirement and disability insurance programs for their intended populations and prevent across-the-board benefits cuts that will otherwise occur as soon as next year for disability insurance beneficiaries.