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.
You already earned significant salary this year and have a large RSU vest coming. You want to know whether Social Security tax still applies to the vest, how much FICA to expect on your pay stub, and how Medicare differs from the Social Security wage cap.
What you need before using this
- Last pay stub before the with YTD Box 3 (Social Security wages) or equivalent.
- confirmation with total for the upcoming .
- Filing status for Additional Medicare threshold math.
- Tax year you are modeling (supported years load SSA wage base from config).
- from prior year if estimating a early in the new year.
Payroll rounding and employer system quirks may differ slightly. Wage base and rates come from tax-year config, not user guesses.
Start here
Planning estimate
Rough estimate for planning, not a filing number. Check your pay stubs, W-2, and a tax pro before you rely on it.
We do not pre-fill personal financial values. Estimates appear only after you enter your own numbers.
Enter your details to estimate
Add your equity, income, state, and withholding details to see an educational estimate. No personal financial values are pre-filled.
Start with the fields below.
Your details
Enter your own numbers below. This is an estimate, not a filing position.
Calculators pull rates from our tax-year files. For the most complete defaults, use 2025. Unloaded years ask you to enter rates yourself.
Total fair market value of shares delivering on this vest date.
Required to estimate
Salary, bonus, and prior vests already counted toward the wage base — from pay stub YTD Box 3 or equivalent.
Required to estimate
For Additional Medicare threshold only. Defaults to SS wages YTD if blank.
Results will appear here once you enter the required details on the left.
Related guides
- 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 Tax Calculator
Model federal and state taxes on your RSU vest, compare withholding to estimated tax, and see what you may keep.
- RSUs on W-2: What to Look For
Your W-2 should reflect RSU vest income in wages — know which boxes to check before filing.
When to use this calculator
- You earn high salary and have a large late in the year — you want to know if Social Security tax still applies.
- Your pay stub showed $0 Social Security on a and you want to verify that matches the wage base rules.
- You are comparing FICA on multiple vests after updating YTD Social Security wages.
Inputs you need
- from confirmation.
- Social Security wages YTD before the from pay stub Box 3 or equivalent.
- Tax year (supported years load SSA wage base from config).
- Filing status if modeling Additional Medicare on the .
How to interpret the result
- Social Security tax applies only to the portion of still under the annual wage base.
- Medicare generally applies to the full — no wage cap.
- Total FICA is Social Security plus Medicare plus any Additional Medicare increment from the .
What this calculator does not know
- Federal or state income tax on the — use the tax calculator for that.
- Employer-side FICA or payroll rounding differences.
- Self-employment tax or non-US payroll.
- Exact YTD wages if pay stubs are unavailable — you must supply a reasonable estimate.
Documents to verify before filing
- Pay stub YTD Social Security wages before and after .
- confirmation with total .
- Boxes 3–6 at year-end.
Next pages to read
These links are for education and planning. They are not filing instructions and do not replace review of your own documents or a qualified tax professional.
Why this happens
income is wages for FICA purposes when shares deliver — the same as salary and bonus.
Social Security tax applies only up to the annual wage base published for each tax year. Wages above the cap are not subject to Social Security tax.
High earners who max out Social Security on salary before a Q4 may see zero Social Security on the portion even though Medicare still applies.
Medicare tax has no wage cap — generally incurs Medicare on the full amount.
Additional Medicare Tax may apply on wages above filing-status thresholds — large vests can push you over the threshold when combined with salary.
Pay stub FICA lines after should reflect these rules — compare to this estimate.
Prior vests and bonuses count toward YTD Social Security wages before your next .
Self-employment income does not mix with this employee calculator — it models style wages only.
Employers may round slightly differently than this estimate.
Boxes 3 and 4 reconcile cumulative Social Security wages and tax for the year.
State income tax is separate — this tool is payroll FICA only.
Two vests in one year: run the calculator twice, updating YTD wages after the first .
Tax year 2026 may require manual verification if wage base is not loaded in config yet.
FICA on does not reduce tax — it is an additional payroll tax on the same wages.
What to check
- YTD Social Security wages on pay stub before .
- from confirmation.
- Pay stub Social Security tax line after posts.
- Whether you were already at the wage cap.
- Medicare and Additional Medicare lines on stub.
- Boxes 3–6 at year-end vs sum of pay stubs.
- Compare to tax calculator for full income tax plus FICA picture.
- FICA guide for narrative explanation of rules.
Assuming a large RSU vest always means a large Social Security tax line
What to check in your documents
- Pay stub YTD Box 3 before and after .
- confirmation total .
- Boxes 3, 4, 5, and 6.
- SSA wage base announcement for the tax year (sourced in methodology).
Example scenario (hypothetical)
Illustration only, not your tax situation.
Questions people ask
- Do RSU vests count toward the Social Security wage base?
- Yes. is wages for FICA. It counts toward the annual Social Security wage base the same as salary.
- Why was Social Security tax $0 on my RSU vest?
- You may have already reached the wage base on earlier salary, bonus, or vests. Medicare can still apply.
- Where do I find Social Security wages YTD?
- Pay stub year-to-date Box 3 equivalent, or estimate from salary plus prior vests and bonuses.
- Does this calculator include federal income tax?
- No. It models FICA only. Use the tax calculator for income tax and estimates.
- Medicare on RSU vest with no wage cap?
- Correct for standard employee Medicare. Additional Medicare may add 0.9% above thresholds.
- Two RSU vests same year?
- Update YTD Social Security wages after the first before modeling the second.
- Which tax year assumptions does this use?
- Social Security wage base and rates from our tax-year config for the year you select — see assumptions box on the calculator.
- FICA vs income tax withholding on vest?
- Separate pay stub lines. Income tax uses supplemental or aggregate rules; FICA follows wage base rules.
- Self-employed RSU income?
- This tool is for employee vests. Self-employment tax rules differ.
- How does this relate to the RSU tax calculator?
- The tax calculator includes FICA in a full estimate. This tool isolates wage-base math when you want to verify Social Security on a late-year .
When to get help from a tax pro
- Pay stub FICA does not match wage base logic after large .
- Multiple employers and wage base coordination.
- Non-US payroll or treaty situations.
- YTD wages on stub unclear after leave or payroll correction.
Related calculators
- 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.
- Annual RSU Income Estimator
Total your expected RSU ordinary income for the year — a starting point before running detailed tax estimates.
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.
- RSUs on W-2: What to Look For
Your W-2 should reflect RSU vest income in wages — know which boxes to check before filing.
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.
Social Security wage base and FICA rates on RSU vest wages from tax-year config.
- SSA Contribution and Benefit Base
Social Security Administration · Official
Annual Social Security wage base used for employee Social Security tax.
- 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 Topic 560 — Additional Medicare Tax
Internal Revenue Service · Official
Additional Medicare Tax thresholds and 0.9% rate on wages above limits.
- 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.