The Social Security Trust Funds are the Old-Age and Survivors Insurance (OASI) and the Disability Insurance (DI) Trust Funds. These funds are accounts managed by the Department of the Treasury. They serve two purposes: (1) they provide an accounting mechanism for tracking all income to and disbursements from the trust funds, and (2) they hold the accumulated asset reserves. These accumulated reserves provide automatic spending authority to pay benefits. The Social Security Act limits trust fund expenditures to benefits and administrative costs.

Benefits to retired workers and their families, and to families of deceased workers, are paid from the OASI Trust Fund. Benefits to disabled workers and their families are paid from the DI Trust Fund. Benefit payments accounted for about 99 percent of the total cost of the combined OASI and DI funds in calendar year 2023.

A Board of Trustees oversees the financial operations of the trust funds. The Board reports annually to the Congress on the financial status of the trust funds.

By law, income to the trust funds must be invested, on a daily basis, in securities guaranteed as to both principal and interest by the Federal government. All securities held by the trust funds are "special issues" of the United States Treasury. Such securities are available only to the trust funds.

In the past, the trust funds have held marketable Treasury securities, which are available to the general public. Unlike marketable securities, special issues can be redeemed at any time at face value. Marketable securities are subject to the forces of the open market and may suffer a loss, or enjoy a gain, if sold before maturity. Investment in special issues gives the trust funds the same flexibility as holding cash.

Data on trust fund investments provide a breakdown by interest rate and trust fund for any month after 1989.

The rate of interest on special issues is determined by a formula enacted in 1960. The rate is determined at the end of each month and applies to new investments in the following month.

The numeric average of the 12 monthly interest rates for 2023 was 4.125 percent. The annual effective interest rate (the average rate of return on all investments over a one-year period) for the OASI and DI Trust Funds, combined, was 2.387 percent in 2023. This lower effective rate resulted because the funds hold special-issue bonds acquired in past years when interest rates were lower.

Tax income is deposited on a daily basis and is invested in "special-issue" securities. The cash exchanged for the securities goes into the general fund of the Treasury and is indistinguishable from other cash in the general fund.

Money to cover program cost (mainly benefit payments) from the trust funds comes from the redemption or sale of securities held by the trust funds. When "special-issue" securities are redeemed, interest is paid. In fact, the principal amount of special issues redeemed, plus the corresponding interest, is just enough to cover the required cost.

The amount bought in 2023 was $1,565 billion, while the amount sold was $1,607 billion. See investment transactions for more detail and earlier years.

Money flowing into the trust funds is invested in U. S. Government securities. Because the government spends this borrowed cash, some people see the trust fund asset reserves as an accumulation of securities that the government will be unable to make good on in the future. Without legislation to restore long-range solvency of the trust funds, redemption of long-term securities prior to maturity would be necessary.

Far from being "worthless IOUs," the investments held by the trust funds are backed by the full faith and credit of the U. S. Government. The government has always repaid Social Security, with interest. The special-issue securities are, therefore, just as safe as U.S. Savings Bonds or other financial instruments of the Federal government.

Many options are being considered to restore long-range trust fund solvency. These options are being considered now, well in advance of the year the trust fund reserves are likely to be depleted. It is thus likely that legislation will be enacted to restore long-term solvency, making it unlikely that the trust funds' securities will need to be redeemed on a large scale prior to maturity.

In the annual Trustees Report, projections are made under three alternative sets of economic, demographic, and programmatic assumptions. Under one of these sets (labeled "Low Cost") in the 2024 Trustees Report, the combined trust funds would be temporarily depleted before returning to positive levels by the end of the 75 year projection period. Under the other two sets (the "Intermediate" and "High Cost") in the 2024 Trustees Report, the combined trust fund reserves become depleted within the next 15 years. The intermediate assumptions reflect the Trustees' best estimate of future experience.

Some benefits could be paid even if the trust fund reserves are depleted. For example, under the intermediate assumptions, annual income to the trust funds is projected to equal about eighty percent of program cost once the trust fund reserves become depleted. If no legislation has been enacted to restore long-term solvency by that time, about three-quarters of scheduled benefits could be paid in each year thereafter.

The Trustees believe that extensive public discussion and analysis of the long-range financing problems of the Social Security program are essential in developing broad support for changes to restore the long-range balance of the program.

The reserves of the larger trust fund (OASI), from which retirement benefits are paid, were nearly depleted in 1982. No beneficiary was shortchanged because the Congress enacted temporary emergency legislation that permitted borrowing from other Federal trust funds and then later enacted legislation to strengthen OASI Trust Fund financing. The borrowed amounts were repaid with interest within 4 years.