Social Security funds are invested entirely in special-issue U.S. Treasury securities backed by the full faith and credit of the federal government. By law, the program cannot hold stocks, corporate bonds, real estate, or any other private asset. At the close of 2024, the two Social Security trust funds together held roughly $2.72 trillion in these government-only securities, earning interest tied to long-term Treasury yields.
What Special-Issue Treasury Securities Are
The Managing Trustee is required by statute to invest any money not needed for current benefit payments, and the law limits those investments to interest-bearing obligations of the United States or obligations guaranteed by the United States as to both principal and interest. Nothing else qualifies.1Office of the Law Revision Counsel. 42 USC 401 – Trust Funds
In practice, that means “special issues” created exclusively for the trust funds. You cannot buy these at a Treasury auction or on any secondary market. Regular investors purchase marketable Treasury bills, notes, and bonds; the trust funds receive non-marketable instruments issued directly to them by the Treasury.2Social Security Administration. Trust Fund FAQs
The key advantage of special issues over marketable bonds is flexibility. A regular Treasury bond can lose value if you sell it before maturity after interest rates have risen. Special issues can be redeemed at face value at any time, which gives the trust funds the functional equivalent of holding cash while still earning interest. Principal and interest carry the same full-faith-and-credit guarantee behind every other Treasury obligation.
Maturity Structure
Special-issue bonds carry maturity dates ranging from one to fifteen years. The Treasury staggers them so that roughly one-fifteenth of the portfolio matures each year, creating a ladder. Short-term certificates of indebtedness, which mature the following June 30, handle day-to-day cash management. That laddered structure smooths interest rate swings over time rather than locking the entire portfolio into whatever rate happens to prevail in a single year.3Social Security Administration. Effective Annual Interest Rates
How the Interest Rate Is Set
The interest rate on new special issues is recalculated at the start of each month. The formula takes the average market yield on all outstanding marketable Treasury securities that will not mature or be called for at least four years, measured at the end of the previous month. If the result is not a clean multiple of one-eighth of a percent, it gets rounded to the nearest one.4Social Security Administration. Interest Rate Formula for Special Issues
That ties the trust funds’ return to the broader long-term government debt market. In 2025, the average interest rate on special issues in the portfolio stood at 4.3 percent, while the effective rate, which accounts for the timing of cash flows and reinvestments, was 2.6 percent.5Social Security Administration. Average and Effective Interest Rates
The gap between those two numbers reflects the fact that the portfolio still holds older securities issued when rates were much lower. As those low-rate bonds mature and get replaced at current rates, the effective rate gradually catches up.
Why Not Stocks or Other Investments
This is the question most people are really asking. The short answer: Congress decided that Social Security reserves should carry zero market risk, and that restriction is written into the statute.1Office of the Law Revision Counsel. 42 USC 401 – Trust Funds
The trust funds exist to guarantee a floor of income for retirees, survivors, and disabled workers. Equity investments would mean that a market crash could shrink the reserves right when they are needed most, during a recession when unemployment rises and payroll tax revenue drops at the same time. Government securities do not have that problem because they can always be redeemed at face value.
The tradeoff is lower returns. Stocks have historically outperformed Treasury bonds by a wide margin. Various reform proposals have tried to capture that premium: some would let the trust funds invest directly in index funds overseen by an independent board, others would create individual accounts where workers invest a portion of their payroll taxes themselves. None have become law. The tension is straightforward. Higher expected returns come with the possibility of losses, and Social Security promises defined benefits regardless of market conditions.
How Securities Get Cashed In for Benefits
When monthly payroll tax revenue falls short of what is needed to pay benefits, the Treasury redeems special issues to cover the gap. Because every dollar of trust fund income is invested immediately upon receipt, some redemption is routine even in months when the program is broadly solvent.
The redemption follows a set hierarchy. Securities with the earliest maturity date go first. If two securities share the same maturity date, the one with the lower interest rate is redeemed first. For securities matching on both date and rate, the oldest purchase is redeemed first. That approach produces a roughly neutral outcome over time: sometimes the redeemed securities carry rates below current yields, sometimes above.6Social Security Administration. Actuarial Note 142 – Trust Fund Investment Policies and Practices
The process happens behind the scenes. Monthly checks and direct deposits continue on schedule regardless of whether the money comes from current tax receipts or redeemed securities.
What the Trust Funds Hold Now
Payroll tax revenue lands in two separate accounts at the U.S. Treasury, each created by federal statute. The Old-Age and Survivors Insurance Trust Fund (OASI) receives the larger share and pays retirement and survivor benefits. The Disability Insurance Trust Fund (DI) receives a smaller allocation and covers benefits for people with qualifying long-term disabilities.1Office of the Law Revision Counsel. 42 USC 401 – Trust Funds
Keeping them separate matters because the two programs face very different financial futures. At the end of 2024, OASI held roughly $2.54 trillion and DI held about $183 billion. Those balances represent the accumulated surplus of decades of tax collections over benefit payments. They are not sitting idle. Virtually every dollar is invested in special issues immediately upon receipt.7Social Security Administration. A Summary of the 2025 Annual Reports
What Happens When the Reserves Run Out
Under the 2025 Trustees Report, the OASI trust fund is projected to exhaust its reserves in 2033. At that point, incoming payroll taxes would still cover about 77 percent of scheduled benefits. The combined OASI and DI funds, if Congress were to allow them to be pooled, would last until 2034 and cover about 81 percent of scheduled benefits afterward. DI on its own is projected to remain solvent through at least 2099.7Social Security Administration. A Summary of the 2025 Annual Reports
Depletion does not mean zero benefits. It means the trust funds can no longer supplement payroll tax revenue, so benefits would have to be trimmed to match what the tax brings in each year unless Congress acts first. The program has no legal authority to borrow or run a deficit. Social Security would still collect hundreds of billions annually in payroll taxes after depletion. The gap between scheduled benefits and available revenue is the issue, not a shutdown.