Social Security funding comes from three sources: payroll taxes paid by workers and their employers, interest earned on the program’s trust fund reserves, and federal income taxes that some beneficiaries pay on their Social Security checks. In 2024, payroll taxes provided roughly 90 percent of the program’s income, interest earnings about 5 percent, and taxation of benefits about 4 percent. The system runs on a pay-as-you-go basis, meaning money collected from today’s workforce flows out almost immediately to today’s retirees, survivors, and disabled beneficiaries, with any surplus held in dedicated trust funds.
Payroll Taxes Do Almost All the Work
The dominant funding stream is the Federal Insurance Contributions Act tax, or FICA. Every worker covered by Social Security has 6.2 percent of their wages withheld for the Old-Age, Survivors, and Disability Insurance program, and the employer pays a matching 6.2 percent on the same wages. Combined, that’s 12.4 percent going into Social Security on every covered paycheck.1Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax2Office of the Law Revision Counsel. 26 USC 3111 – Rate of Tax
Not every dollar of wages is taxed. In 2026, only the first $184,500 of earnings is subject to Social Security tax. Anything above that ceiling is exempt. The most any single worker will contribute in 2026 is $11,439, with the employer paying the same.3Social Security Administration. Contribution and Benefit Base The cap adjusts each year based on changes in the national average wage index, so it generally rises over time. Workers who hold multiple jobs and end the year over the cap in combined wages can claim a refund for the excess withholding on their tax return.4Social Security Administration. Social Security Tax Limits on Your Earnings
Medicare is funded through a separate tax on the same pay stub and flows to a different trust fund. It is not part of Social Security’s funding.5Internal Revenue Service. Topic No. 751, Social Security and Medicare Withholding Rates
Self-Employed Workers Pay Both Halves
If you work for yourself, there’s no employer to cover the other 6.2 percent. Under the Self-Employment Contributions Act, self-employed workers pay the full 12.4 percent on their net earnings, up to the same $184,500 cap.6Office of the Law Revision Counsel. 26 USC 1401 – Rate of Tax3Social Security Administration. Contribution and Benefit Base
The tax code softens that by letting self-employed filers deduct half of their self-employment tax when calculating adjusted gross income. This mirrors the fact that traditional employees never pay income tax on the employer-paid half of FICA.7Office of the Law Revision Counsel. 26 USC 164 – Taxes The tax is reported on Schedule SE with Form 1040, and the deduction runs through Schedule 1.8Internal Revenue Service. Topic No. 554, Self-Employment Tax Self-employed workers pay in through quarterly estimated payments rather than paycheck withholding.
Interest on the Trust Fund Reserves
Money collected through payroll and self-employment taxes flows into two accounts held at the U.S. Treasury: the Old-Age and Survivors Insurance Trust Fund, which pays retirees and their families, and the Disability Insurance Trust Fund, which pays workers with qualifying disabilities.9Social Security Administration. A Summary of the 2025 Annual Reports
By law, any surplus not needed for immediate benefit payments has to be invested in special-issue U.S. Treasury securities backed by the full faith and credit of the federal government. These come in two forms. Short-term certificates mature every June 30. Longer-term bonds carry maturities from one to fifteen years. When the trust funds need cash, securities are redeemed starting with those closest to maturity and carrying the lowest interest rate.10Social Security Administration. Special Issue Securities
The interest those securities earn is the program’s second revenue stream. For fiscal year 2026, the combined trust funds are projected to earn roughly $66.6 billion in net interest, which gets credited back to the funds and helps cover benefit payments in years when tax revenue alone falls short.11Social Security Administration. Fiscal Year Historical and Projected Trust Fund Operations Through 2034
Federal Income Taxes on Benefits
The third source is federal income tax that some beneficiaries pay on their Social Security checks. Whether your benefits are taxable depends on your “combined income,” which is your adjusted gross income, plus any nontaxable interest, plus half of your Social Security benefits. Two thresholds apply:
- If combined income is between $25,000 and $34,000 for a single filer, or $32,000 to $44,000 for a married couple filing jointly, up to half of benefits may be taxable.
- Above $34,000 single or $44,000 joint, up to 85 percent of benefits may be taxable.
These figures are set by statute and have never been indexed for inflation, so more retirees cross them every year.12Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits
The revenue this generates doesn’t go into the general treasury. It’s routed back into the Social Security trust funds, creating a small feedback loop within the program. Each January, the Social Security Administration mails beneficiaries a Form SSA-1099 showing the prior year’s total benefits for use on the tax return.13Social Security Administration. Get Your Social Security Benefit Statement (SSA-1099) Beneficiaries who prefer to have tax withheld directly from their checks can file Form W-4V with the SSA and pick a rate of 7, 10, 12, or 22 percent.14IRS.gov. Form W-4V Voluntary Withholding Request
What Happens When the Reserves Run Down
The two trust funds are on different tracks. The Disability Insurance Trust Fund can pay full benefits through at least 2099, the last year the 2025 Trustees Report projects.9Social Security Administration. A Summary of the 2025 Annual Reports
The retirement side is tighter. The Old-Age and Survivors Insurance Trust Fund is projected to exhaust its reserves by 2033. After that, incoming payroll taxes would still cover about 77 percent of scheduled benefits, with the remaining 23 percent unfunded absent congressional action.9Social Security Administration. A Summary of the 2025 Annual Reports The payroll tax pipeline keeps flowing regardless, so the program does not disappear at that point, but retirees could face an automatic reduction unless lawmakers raise taxes, cut benefits, or combine the two.