No. OASDI is not included in federal income tax withholding. The two deductions sit next to each other on your paycheck, but they are separate taxes with separate rates, separate purposes, and separate boxes on your W-2. Federal income tax withholding is an advance payment on the income tax you will owe when you file your return. OASDI, short for Old-Age, Survivors, and Disability Insurance, is the Social Security portion of your FICA payroll tax.
How to Tell Them Apart on Your Paycheck
On a pay stub, federal income tax withholding usually appears as “Federal Withholding” or “FIT.” OASDI shows up on its own line, often labeled “Social Security” or “OASDI.” Medicare, the other half of FICA, has its own line too. Three line items, three different taxes.
Your W-2 keeps them in separate boxes:1Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3
- Box 2: federal income tax withheld
- Box 3: wages subject to Social Security tax, capped at $184,500 for 2026
- Box 4: Social Security (OASDI) tax withheld
- Box 5: wages subject to Medicare tax, no cap
- Box 6: Medicare tax withheld
Box 4 should never exceed $11,439 for 2026, and Box 3 should never exceed $184,500. If either is too high, your employer over-withheld and needs to correct it.1Internal Revenue Service. 2026 General Instructions for Forms W-2 and W-3
What Each Tax Pays For
Federal income tax withholding feeds the government’s general fund, which covers everything from defense to national parks. The requirement comes from 26 U.S.C. ยง 3402, which directs every employer paying wages to withhold tax according to IRS tables.2Office of the Law Revision Counsel. 26 USC 3402 – Income Tax Collected at Source
OASDI dollars go somewhere different. They flow into the dedicated Old-Age and Survivors Insurance and Disability Insurance trust funds, which pay Social Security retirement, survivor, and disability benefits. Medicare withholding goes into the Hospital Insurance trust fund. Congress cannot redirect that money to other programs.
How the Amounts Are Calculated
Federal income tax withholding is variable. It depends on how much you earn and what you put on your Form W-4: filing status, credits for dependents, and any extra withholding you request per pay period.3Internal Revenue Service. Form W-4 (2026) Your employer runs those entries through the withholding tables in IRS Publication 15-T to produce the deduction each paycheck.4Internal Revenue Service. Publication 15-T (2026), Federal Income Tax Withholding Methods Two employees earning the same salary can have very different income tax withheld because their W-4 entries differ.
OASDI is a flat percentage. The rate is 6.2% of your wages up to the annual Social Security wage base, which for 2026 is $184,500.5Internal Revenue Service. Publication 15 (2026), (Circular E), Employer’s Tax Guide Once your year-to-date earnings hit that ceiling, OASDI withholding stops for the rest of the year. Filing status and dependents do not change the rate.6Office of the Law Revision Counsel. 26 USC 3101 – Rate of Tax Your employer pays a matching 6.2% on your behalf.7Office of the Law Revision Counsel. 26 USC 3111 – Rate of Tax
Medicare, the HI half of FICA, is 1.45% of all wages with no cap. If your wages exceed $200,000 in a year, an Additional Medicare Tax of 0.9% applies to the excess, and your employer does not match that extra amount.8Internal Revenue Service. Questions and Answers for the Additional Medicare Tax
Only One of These Gets Reconciled at Tax Time
Federal income tax withholding is an estimate. When you file your Form 1040, it is reconciled against what you actually owe: too much withheld means a refund, too little means a balance due. You can adjust your W-4 anytime during the year to get closer to the right number.9Internal Revenue Service. Tax Withholding
OASDI is not reconciled on your return. The amount withheld is final. There is one exception: if you worked for two or more employers in the same year and your combined wages exceeded the $184,500 cap, you probably paid too much OASDI, since each employer withheld without knowing about the other. You can claim the excess as a credit on your tax return.9Internal Revenue Service. Tax Withholding If a single employer over-withheld, that employer must correct it directly.
Why Pre-Tax Deductions Can Reduce One and Not the Other
This is where people most often get tripped up, and it is why the numbers in Box 1, Box 3, and Box 5 of a W-2 often disagree.
A traditional 401(k) contribution lowers the wages reported for federal income tax (Box 1) but does not reduce the wages subject to Social Security or Medicare (Boxes 3 and 5).10Internal Revenue Service. Retirement Plan FAQs Regarding Contributions – Are Retirement Plan Contributions Subject to Withholding for FICA, Medicare or Federal Income Tax So your 401(k) cuts your income tax withholding but not your OASDI.
Benefits paid through a Section 125 cafeteria plan behave differently. Health insurance premiums, dental coverage, and dependent care paid through a pre-tax salary reduction under a cafeteria plan are excluded from both income tax wages and FICA wages.11Social Security Administration. Cafeteria Benefit Plans Those deductions do reduce your OASDI.
What to Check
Pull a recent pay stub and look for three separate line items: federal income tax withholding, OASDI (or Social Security), and Medicare. If any of them are lumped together, raise it with your payroll department. In January, check your W-2 and confirm Box 4 does not exceed the annual OASDI maximum and Box 3 does not exceed the wage base. If you held more than one job during the year and your combined Box 3 wages crossed $184,500, flag the excess OASDI as a credit when you file.