Social Security is funded mainly by payroll taxes paid by workers and their employers, with two smaller streams filling out the picture: federal income tax that beneficiaries pay on their own benefits, and interest earned on the money the program has already set aside. In 2024, payroll taxes supplied about 91% of the program’s income, benefit taxation about 4%, and interest earnings the remaining 5%.1Social Security Administration. Financial Operations of the Trust Funds Money in equals money out on a rolling basis: today’s workers pay for today’s retirees, survivors, and disabled beneficiaries.
Payroll Taxes on Wages
The Federal Insurance Contributions Act (FICA) sets the Social Security payroll tax at 6.2% of covered wages for the employee and a matching 6.2% for the employer, a combined 12.4%.2Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax3Office of the Law Revision Counsel. 26 USC 3111 – Rate of Tax Employers withhold the worker’s share from each paycheck and send it to the federal government along with the employer match.
Only wages up to an annual ceiling are taxed. The contribution and benefit base, usually called the wage base, is $184,500 for 2026.4Social Security Administration. Contribution and Benefit Base Earnings above that figure in a single year are not subject to the Social Security portion of FICA. The wage base is reset every year based on the national average wage index.
Self-Employment Taxes
Independent contractors, freelancers, and sole proprietors pay into Social Security through the Self-Employment Contributions Act (SECA) rather than FICA. Without an employer to cover half, a self-employed worker owes the full 12.4% rate.5Office of the Law Revision Counsel. 26 USC Chapter 2 – Tax on Self-Employment Income The same $184,500 wage base applies, and the tax begins only when net self-employment earnings reach at least $400 for the year.4Social Security Administration. Contribution and Benefit Base
The 12.4% rate does not apply to your full net profit. You first multiply net self-employment earnings by 92.35%, then apply the rate to that reduced figure.6Internal Revenue Service. Topic No. 554, Self-Employment Tax The adjustment mirrors the fact that traditional employees do not pay FICA on the employer’s share. Self-employed filers can also deduct half of their SECA tax when figuring adjusted gross income, which reduces income tax but not the self-employment tax itself.7Internal Revenue Service. Self-Employment Tax (Social Security and Medicare Taxes)
Reporting self-employment income is not just a tax obligation. Earnings that never get reported never post to your Social Security record, and because future benefits are calculated from your lifetime earnings, unreported income lowers the check you would eventually receive.
How These Taxes Turn Into Benefits
Every dollar of FICA or SECA also buys work credits, and credits are what determine whether you qualify for retirement benefits at all. Eligibility takes 40 credits, and you can earn up to four in a year, so at least ten years of covered work is required.8Social Security Administration. Social Security Credits and Benefit Eligibility
In 2026, one credit costs $1,890 in covered earnings, and $7,560 in a year gets you the maximum four.9Social Security Administration. Quarter of Coverage The dollar figure resets each year with average wages. Credits do not expire; time away from work does not erase what you already have.
Income Tax on Benefits
Some retirees owe federal income tax on part of their Social Security checks, and that tax revenue is one of the program’s funding streams. Whether benefits are taxed depends on combined income, which the IRS defines as adjusted gross income plus any tax-exempt interest plus half of annual Social Security benefits.10Internal Revenue Service. Social Security Income
The taxable share turns on two thresholds set by filing status:
- Single filers with combined income between $25,000 and $34,000 can have up to 50% of benefits taxed; above $34,000, up to 85%.11Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits
- Married filing jointly uses $32,000 and $44,000, with the same 50% and 85% tiers.11Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits
- Married filing separately while living with a spouse has a base amount of $0, so benefits are taxable from the first dollar of combined income.11Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits
Those dollar figures are fixed in the statute and are not indexed for inflation. They have not changed since 1984, so more beneficiaries fall into the taxable range each year as wages and benefit amounts rise. The money collected does not flow to the general fund. Federal law directs it into the Old-Age and Survivors Insurance (OASI) and Disability Insurance (DI) trust funds.12Office of the Law Revision Counsel. 42 USC 401 – Trust Funds
Interest on Trust Fund Reserves
When tax collections in a year run higher than benefit payments, the surplus is held in the OASI and DI trust funds. Federal law does not let those reserves sit as cash. The Managing Trustee must invest them in interest-bearing obligations backed by the full faith and credit of the United States.12Office of the Law Revision Counsel. 42 USC 401 – Trust Funds
In practice, that means special-issue Treasury bonds created only for the trust funds. Each bond’s interest rate equals the average market yield on all outstanding marketable Treasury securities with at least four years left to maturity, rounded to the nearest one-eighth of one percent.13Social Security Administration. Interest Rate Formula The interest the government pays on those bonds flows back into the trust fund balances.
Will These Funding Sources Keep Up With Benefits?
The 2025 Annual Trustees Report projects that the OASI trust fund, which pays retirement and survivor benefits, will run out of reserves in 2033.14Social Security Administration. Status of the Social Security and Medicare Programs – A Summary of the 2025 Annual Reports Depletion is not a shutdown. Payroll taxes and taxes on benefits keep coming in, and at that point they would cover roughly 77% of scheduled benefits.
Considered together on a hypothetical combined basis, the OASI and DI trust funds are projected to be depleted in 2034, with incoming revenue then able to pay about 81% of scheduled benefits.14Social Security Administration. Status of the Social Security and Medicare Programs – A Summary of the 2025 Annual Reports The long-range shortfall is estimated at 3.95% of taxable payroll. Closing it entirely would take some mix of higher taxes, lower benefits, or changed eligibility rules, and Congress has not yet enacted legislation to do so.