The most common abbreviation for Social Security is SS. It’s informal shorthand for the program itself, and you’ll see it in casual references, on some pay stubs, and in everyday conversation. The trouble is that Social Security documents rarely stop at “SS.” Your paycheck, tax forms, and benefit statements pull from a whole family of related abbreviations — SSA, SSN, OASDI, FICA, SSDI, SSI, and a few more — and each one points to a different piece of the system.
SS, SSA, and SSN
SS is the plain shorthand for Social Security. It isn’t an official government acronym, but everyone understands it.
SSA is the Social Security Administration, the independent federal agency that runs the program. The SSA handles retirement, disability, and survivor benefits, enrolls people in Medicare, and issues Social Security numbers and cards.1Social Security Administration. About Social Security When you log into an online account to check your earnings record or apply for benefits, you’re dealing with the SSA.
SSN is your Social Security Number, the nine-digit identifier assigned to U.S. citizens, permanent residents, and certain temporary residents.2Social Security Administration. Social Security History – Social Security Numbers The SSN follows you through most financial and tax paperwork you’ll ever fill out.
OASDI, FICA, and SECA on Your Pay Stub
OASDI stands for Old-Age, Survivors, and Disability Insurance. It’s the formal name of the Social Security tax withheld from your paycheck, and it covers exactly what the name says: retirement, payments to surviving family members, and disability benefits. The program lives in Subchapter II of the Social Security Act.3Office of the Law Revision Counsel. 42 USC Ch 7 – Social Security Your pay stub may print this line as “OASDI,” “SS Tax,” or “Social Security.” Whatever the label, the rate is 6.2 percent of gross wages, matched by 6.2 percent from your employer.4Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax For 2026, the tax applies only to the first $184,500 you earn.5Social Security Administration. Contribution and Benefit Base
FICA stands for the Federal Insurance Contributions Act, the law requiring both the OASDI tax and the Medicare tax to be withheld from your wages. FICA is the umbrella; OASDI is one piece of it. The other piece is the Hospital Insurance tax, abbreviated HI and commonly called the Medicare tax, at 1.45 percent with no earnings cap and a matching 1.45 percent from your employer. Wages above $200,000 in a calendar year ($250,000 for joint filers) trigger an additional 0.9 percent Medicare surtax on the excess, which the employer does not match.4Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax
SECA stands for the Self-Employment Contributions Act. Self-employed people pay both the employee and employer shares of Social Security and Medicare, but get to deduct half of the total as a business expense.6Social Security Administration. What Are FICA and SECA Taxes?
SSDI vs. SSI
These two abbreviations look almost identical, both involve disability, and they get confused constantly. They are different programs with different rules.
SSDI: Social Security Disability Insurance
SSDI pays monthly benefits to workers who become disabled after earning enough work credits by paying into Social Security over the years.7Social Security Administration. How Does Someone Become Eligible? The payment amount depends on your lifetime earnings, not on financial need. To qualify, the SSA has to find that you can’t perform substantial gainful activity because of a medical condition expected to last at least 12 months or result in death. For 2026, substantial gainful activity means earning more than $1,690 per month, or $2,830 if you’re blind.8Social Security Administration. What’s New in 2026? – The Red Book
SSI: Supplemental Security Income
SSI is a needs-based program for people who are aged, blind, or disabled and have very limited income and resources. There is no work-history requirement, and the money comes from general tax revenue rather than payroll taxes. The maximum federal SSI payment for 2026 is $994 per month for an individual and $1,491 for a couple, and many states add their own supplement.9Social Security Administration. SSI Federal Payment Amounts
Some people qualify for both SSDI and SSI at the same time.
AIME, PIA, and COLA on Your Benefit Statement
AIME is your Average Indexed Monthly Earnings. The SSA takes your highest 35 years of earnings, adjusts older wages for inflation, and averages them into a monthly figure. That figure is the starting point for your benefit.
PIA is your Primary Insurance Amount, the monthly benefit you would receive if you claimed at full retirement age. The SSA calculates it by running your AIME through a three-tier formula. For workers first eligible in 2026, the PIA equals 90 percent of the first $1,286 of AIME, plus 32 percent of AIME between $1,286 and $7,749, plus 15 percent of any AIME above $7,749.10Social Security Administration. Primary Insurance Amount Claiming early reduces the payment below the PIA. Delaying past full retirement age increases it.
COLA is the annual Cost-of-Living Adjustment. Each year the SSA adjusts benefits to keep pace with inflation. The 2026 COLA is 2.8 percent, which raised the average monthly retirement benefit to roughly $2,071 and applies to SSI as well.11Social Security Administration. 2026 Cost-of-Living Adjustment (COLA) Fact Sheet12Social Security Administration. Cost-of-Living Adjustment (COLA) Information
SSN vs. ITIN
One boundary worth naming: not every taxpayer has an SSN. Nonresident and resident aliens who aren’t eligible for a Social Security Number get an ITIN from the IRS instead, short for Individual Taxpayer Identification Number. An ITIN has the same nine-digit format as an SSN but always starts with the digit 9.13Internal Revenue Service. Taxpayer Identification Numbers
An ITIN is strictly for tax processing. It doesn’t grant work authorization, doesn’t make you eligible for Social Security benefits, and doesn’t qualify you for the earned income credit. Anyone eligible for an SSN is expected to use the SSN.13Internal Revenue Service. Taxpayer Identification Numbers
Quick Reference
- SS: Social Security (informal shorthand for the program)
- SSA: Social Security Administration (the federal agency)
- SSN: Social Security Number (your nine-digit identifier)
- OASDI: Old-Age, Survivors, and Disability Insurance (the formal name for the Social Security tax and benefits)
- FICA: Federal Insurance Contributions Act (the law requiring OASDI and Medicare payroll taxes)
- SECA: Self-Employment Contributions Act (the self-employed equivalent of FICA)
- HI: Hospital Insurance (the Medicare portion of payroll tax)
- SSDI: Social Security Disability Insurance (disability benefits earned through work credits)
- SSI: Supplemental Security Income (needs-based benefits for aged, blind, or disabled individuals)
- AIME: Average Indexed Monthly Earnings (the earnings average used to calculate your PIA)
- PIA: Primary Insurance Amount (your calculated monthly benefit at full retirement age)
- COLA: Cost-of-Living Adjustment (the annual inflation adjustment to benefits)
- ITIN: Individual Taxpayer Identification Number (a tax-only ID for people ineligible for an SSN)