Social Security Trust Fund

The Social Security trust funds are the accounts the federal government uses to track Social Security's income and outgo, authorized under Section 201 of the Social Security Act. There are two: the Old-Age and Survivors Insurance (OASI) Trust Fund, which pays retirement and survivor benefits, and the Disability Insurance (DI) Trust Fund. Social Security payroll taxes are credited to the funds, benefits and administrative costs are paid from them, and any excess is invested, as the law requires, in special non-marketable U.S. Treasury securities that earn interest. The funds are a bookkeeping and legal structure, not a stockpile of currency and not an individual account.

Understanding the trust funds means separating the mechanism from three common misreadings. First, Social Security is largely pay-as-you-go: most of the taxes collected in a year are paid out as benefits that same year, so the fund balances hold reserves rather than each worker's own lifetime contributions. Nothing in the funds is earmarked to a particular person. Second, when the funds ran surpluses, the law required investing them in special-issue Treasury securities. Critics call these "just IOUs," but they are interest-bearing obligations of the United States, backed by the same full faith and credit as the Treasury bonds held by any investor; the government owes the funds this money the way it owes any bondholder. Third, "trust fund" does not imply a segregated cash vault: the reserves exist as securities, and the interest they earn is itself part of the funds' income.

The two funds are legally distinct, which is why projections often report OASI and DI separately, and why a combined "OASDI" figure is described as hypothetical, since spending one fund's reserves to cover the other requires a law that does not currently exist. What the trust funds cannot answer on their own is the question people most often attach to them, namely whether income and reserves will be enough to pay scheduled benefits in the decades ahead. That outlook, including projected reserve-depletion dates and the share of benefits that would remain payable, is the subject of Social Security solvency.

Money moves through the trust funds in a repeating annual cycle.

1. Income in: Social Security payroll taxes on covered wages, taxes some beneficiaries pay on their benefits, and interest earned on the funds' securities are credited to OASI and DI.

2. Investment: any reserves not immediately needed are invested by law in special-issue U.S. Treasury securities, which earn interest that returns to the funds.

3. Outgo: monthly benefits and administrative costs are paid from the appropriate fund, OASI for retirement and survivor benefits and DI for disability benefits.

4. Reserves: if income exceeds outgo, reserves rise; if outgo exceeds income, the funds redeem securities to cover the gap, and reserves fall.

A conceptual example. In a year when payroll taxes and benefit taxes bring in slightly less than benefits paid, the shortfall is covered by redeeming some of the funds' Treasury securities plus the interest they earned. The reserves act as a buffer smoothing income against outgo; they are not a pile of set-aside cash and not tied to any individual worker's record.