Your RSU vest pay stub shows little or no Social Security tax, or FICA on the vest looks lower than on salary. You earn enough that salary may have already hit the Social Security wage cap, or a large vest lands late in the year. You want to know how much Social Security tax applies and whether payroll made an error.
Start here
What you need before using this
- Pay stub YTD Social Security wages before (Box 3 YTD on prior stub).
- confirmation with .
- Pay stub from period showing FICA lines.
- SSA wage base for your tax year from official SSA publications.
- Second employer if two jobs same year.
Social Security wage base amounts change annually — verify on SSA.gov for your tax year. This page is educational, not payroll advice.
Why this happens
Social Security tax uses an annual wage base limit updated by SSA each year — not a per-paycheck cap.
adds to Box 3 Social Security wages same as salary and bonus.
Late-year vests often hit after salary already consumed much of the wage base — lower Social Security component on stub.
Medicare tax has no wage base cap — 1.45% employee rate plus possible Additional Medicare Tax on high wages.
Employer withholds Social Security on each paycheck until YTD hits wage base — included.
Two employers may each Social Security on full wages until each reaches cap — overpayment recovered on Form 1040.
Pay stub may show $0 Social Security on when YTD already at cap — normal, not an error.
Income tax on is separate from FICA — flat supplemental rate vs FICA rules.
Self-employment income is different — this page is wages only.
High earners comparing tax estimate should split income tax vs FICA components.
FICA wage base calculator on this site models remaining cap before .
Pub. 15 and SSA wage base publications govern — verify annual cap for filing year.
Additional Medicare Tax uses different thresholds than Social Security wage base.
does not reduce FICA wage base — full was wages before shares sold.
December still counts toward calendar-year wage base for that tax year.
What to check
- YTD Box 3 Social Security wages on pay stub before .
- SSA wage base minus YTD = remaining Social Security taxable room.
- amount vs remaining room under cap.
- Social Security tax line on pay stub — zero may be correct if at cap.
- Medicare tax line on — usually still applies.
- Second employer Box 3 if two jobs.
- Form 1040 excess Social Security tax worksheet if over-withheld.
- Calculator output vs actual stub FICA.
Expecting the same FICA percentage on a December RSU vest as on January salary
What to check in your documents
- Pay stub before and after with YTD FICA.
- confirmation .
- Boxes 3–6 after year-end.
- SSA wage base publication for tax year.
- Second if applicable.
November vest after salary near wage base
Illustration only, not your tax situation.
Questions people ask
- Does RSU vest count toward Social Security wage base?
- Yes — is wages in Box 3. It counts toward the annual cap same as salary.
- No Social Security tax on RSU vest pay stub?
- Possible if YTD wages already reached the wage base. Medicare usually still applies.
- Two jobs and RSU vest Social Security?
- Each employer withholds until cap on their wages. Excess Social Security may be refunded on Form 1040.
- RSU vest vs bonus for wage base?
- Both are wages — both count toward the same annual Social Security wage base.
- Medicare on RSU after Social Security cap?
- Yes — Medicare tax generally applies to all wages without a cap.
- Additional Medicare Tax on RSU vest?
- Large vests contribute to wages that may trigger Additional Medicare Tax — see dedicated guide.
- Which calculator for wage base at vest?
- FICA wage base calculator with YTD wages and expected .
- Employer wrong on FICA at vest?
- Compare pay stub to calculator. Contact payroll if Social Security tax on wages clearly above cap.
- Related guides?
- FICA taxes, Additional Medicare on , pay stub after , effective tax rate.
- Self-employed RSU?
- Employees receive wages — this page covers employee FICA. Self-employment rules differ.
When to get help from a tax pro
- Two employers and Social Security over- exceeds refund worksheet comfort.
- Payroll took Social Security tax on wages clearly above annual cap.
- from foreign employer with unclear FICA treatment.
- Total wages near Additional Medicare thresholds with complex household income.
Related calculators
- RSU FICA Wage Base Calculator
Model FICA on an RSU vest using official wage base and payroll rates — especially when salary already consumed part of the Social Security cap.
- RSU Tax Calculator
Model federal and state taxes on your RSU vest, compare withholding to estimated tax, and see what you may keep.
- RSU Withholding Gap Calculator
Focus on the gap between what your employer withholds on RSU vests and what you may owe when everything is reconciled.
Related pages
- RSUs and FICA Taxes
RSU vest income is usually wages for payroll tax purposes — you may see FICA on your vest pay stub.
- RSUs and Medicare / Additional Medicare Tax
Large RSU vests can push wages over thresholds where additional Medicare tax may apply.
- Reading Your Pay Stub After an RSU Vest
Vest FMV adds to gross wages on the same pay stub as salary — supplemental withholding and FICA lines spike, but net pay alone does not prove your full-year tax is covered.
- RSU Effective Tax Rate Explained
There is no flat RSU tax rate — effective tax on vest FMV includes federal, FICA, and state components that change with your total income.
- Two RSU Vests in the Same Month
Each vest adds full FMV to wages — two same-month vests stack withholding and bracket impact faster than flat supplemental rates may cover.
Sources and notes
Primary tax claims on this page are supported by the official and secondary sources below. Broker and software links describe reporting mechanics — confirm rules against IRS or state guidance.
RSU vest FMV as Social Security wages; annual wage base cap and Medicare without cap.
- SSA — Contribution and Benefit Base
Social Security Administration · Official
Annual Social Security wage base limit for FICA withholding.
- IRS Publication 15 (Circular E) — Supplemental wages
Internal Revenue Service · Official
Section 7 describes supplemental wage withholding, including the optional 22% flat rate and 37% rate above $1 million of supplemental wages in a calendar year.
- IRS Publication 525 — Taxable and Nontaxable Income
Internal Revenue Service · Official
Covers compensation income from stock-based pay, including restricted property under section 83.
For learning, not filing
VestingTax.com is not a CPA firm or tax preparer. Grants, employers, and states all differ. Use the cited IRS and state sources above, your own documents, and a qualified tax professional before you make decisions from this guide.