No. OASDI is not included in federal income tax withholding. It’s a separate payroll tax that funds Social Security, collected under different rules, reported in different boxes on your W-2, and calculated in a completely different way. Both come out of the same paycheck, which is why the two get confused, but they are not the same line of money.
What Federal Income Tax Withholding Is
Federal income tax withholding is an advance payment toward the income tax you’ll owe when you file your Form 1040. The requirement comes from 26 U.S.C. § 3402, which tells employers to withhold from wages using tables the IRS publishes.1Office of the Law Revision Counsel. 26 USC 3402 – Income Tax Collected at Source
The amount depends on what you earn and what you put on Form W-4: your filing status, any dependent credits, and any extra withholding you request per pay period.2Internal Revenue Service. Form W-4 (2026) Your employer runs those choices through the methods in Publication 15-T to produce the number on your stub.3Internal Revenue Service. Publication 15-T (2026), Federal Income Tax Withholding Methods
Because it’s an estimate, income tax withholding gets reconciled on your return. Too much withheld, you get a refund. Too little, you owe. You can change your W-4 during the year to adjust.
What OASDI Is
OASDI stands for Old-Age, Survivors, and Disability Insurance, better known as Social Security. Along with Medicare, it makes up FICA. The money doesn’t go to the general fund the way income tax does; it flows into the Social Security and Medicare trust funds.
OASDI is a flat 6.2% of your wages up to an annual wage base. For 2026, that base is $184,500, which caps employee OASDI withholding at $11,439 for the year.4Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide5Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3 Once you hit the base, OASDI stops for the year. Medicare, the other half of FICA, is 1.45% on every dollar with no ceiling, plus an Additional Medicare Tax of 0.9% on wages above $200,000 in a calendar year.6Social Security Administration. Social Security and Medicare Tax Rates7Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
Your employer matches the 6.2% OASDI and 1.45% Medicare, paying the same amount on your behalf.8Office of the Law Revision Counsel. 26 USC 3111 – Rate of Tax The 0.9% Additional Medicare Tax isn’t matched.
Nothing on your W-4 changes any of this. Filing status, dependents, extra withholding requests — none of it touches OASDI. Two coworkers earning the same salary pay identical OASDI, even if their income tax withholding looks nothing alike.9Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax
How to See the Separation on Your Paycheck and W-2
On a pay stub, the two show up as different line items. Federal income tax withholding usually appears as “Federal Withholding” or “FIT.” OASDI appears as “Social Security” or “OASDI,” with Medicare on its own line. If a stub bundles them together, ask payroll to break it out.
On your annual W-2, they sit in different boxes:5Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3
- Box 2 shows federal income tax withheld.
- Box 3 shows wages subject to Social Security tax, capped at $184,500 for 2026.
- Box 4 shows the OASDI tax withheld, which should not exceed $11,439 for 2026.
- Box 5 shows Medicare wages, with no cap.
- Box 6 shows Medicare tax withheld.
Worth a quick check each January. If Box 3 tops $184,500 or Box 4 tops $11,439, your employer over-withheld and needs to fix it.
Why the Distinction Matters
The practical differences are the reason it’s worth keeping the two straight.
Only One Gets Reconciled at Tax Time
Federal income tax withholding is trued up on your 1040. OASDI is not. What came out of your check is final. The one exception is if you had two or more employers in the same year and your combined wages passed the $184,500 cap; the excess OASDI can be claimed as a credit on your return.10Internal Revenue Service. Tax Withholding If a single employer over-withheld, that employer has to correct it directly.
Pre-Tax Deductions Don’t Treat Them the Same
This trips people up. A traditional 401(k) contribution lowers the wages reported in Box 1 for income tax, but it does not lower Box 3 or Box 5. You still owe OASDI and Medicare on the amount you contributed.11Internal Revenue Service. Retirement Plan FAQs Regarding Contributions
Benefits paid through a Section 125 cafeteria plan — health insurance premiums, dental, dependent care — are different. Those amounts come out of wages for both income tax and FICA, so they actually reduce your OASDI.12Social Security Administration. Cafeteria Benefit Plans Health premiums cut your Social Security tax; 401(k) contributions don’t.
Self-Employed People Pay Both Halves
If you work for yourself, there’s no employer matching anything. Self-employment tax runs 15.3%: 12.4% OASDI and 2.9% Medicare, calculated on Schedule SE. The $184,500 OASDI base still applies, and the 0.9% Additional Medicare Tax kicks in above $200,000 for single filers or $250,000 for married filing jointly.6Social Security Administration. Social Security and Medicare Tax Rates13Social Security Administration. 2026 Cost-of-Living Adjustment (COLA) Fact Sheet You can deduct half of your self-employment tax as an adjustment to income on Schedule 1, which reduces your income tax but not the self-employment tax itself.14Internal Revenue Service. Schedule SE (Form 1040) Even for the self-employed, the two taxes stay separate on the return.
Narrow Cases Where OASDI Doesn’t Apply
Almost every worker pays OASDI. A few exceptions exist, and they’re worth knowing so you don’t assume one covers you when it doesn’t.
Students enrolled at least half-time at a college or university who work for that same institution can be exempt from FICA, provided the job is incidental to their education. Students who receive benefits like retirement contributions, paid vacation, or sick leave are treated as professional employees and don’t qualify.15Internal Revenue Service. Student FICA Exception
Nonresident aliens on F-1, J-1, M-1, or Q-1 visas are exempt from OASDI and Medicare on wages tied to the purpose of the visa. The exemption ends once the person becomes a resident alien for tax purposes.16Internal Revenue Service. Aliens Employed in the U.S. – Social Security Taxes
Members of recognized religious groups conscientiously opposed to insurance benefits can apply for exemption on Form 4029. Approval requires a permanent waiver of Social Security and Medicare benefits.17Internal Revenue Service. Form 4029, Application for Exemption From Social Security and Medicare Taxes and Waiver of Benefits
Outside these narrow categories, OASDI applies, and it applies as its own tax, on its own line, at its own fixed rate — never rolled into your federal income tax withholding.