RSU withholding is not the same thing as your final tax bill. When restricted stock units vest and settle, their value is generally treated as compensation income. Your employer may withhold federal income tax using supplemental-wage rules, but your actual federal tax is calculated later using your entire tax return. If the withholding rate is lower than the tax rate ultimately applying to that additional income, you can owe the difference.
This article focuses on U.S. federal tax rules for employees receiving RSUs in 2026. State taxes, cross-border employment, unusual settlement schedules, and private-company arrangements can change the result.
| Question | Short answer |
|---|---|
| Are RSUs normally taxable when granted? | Usually no. A typical RSU is a promise to deliver stock or cash later. |
| When does income usually arise? | For a typical stock-settled award, around vesting and settlement when the shares are transferred. |
| Is 22% necessarily your RSU tax rate? | No. It can be a withholding rate, not your final marginal or effective tax rate. |
| Can sell-to-cover still leave you owing tax? | Yes. It normally covers the withholding amount calculated by payroll, not necessarily your final tax liability. |
Contents
- Why an RSU tax shortfall happens
- How RSUs are taxed
- How federal withholding works in 2026
- A $100,000 RSU example
- Other reasons your numbers may not match
- How to estimate your potential shortfall
- W-4 adjustments versus estimated payments
- What happens when you sell the shares
Why an RSU Tax Shortfall Can Happen
The crucial distinction is between withholding and tax liability.
Withholding is money sent to the IRS during the year on your behalf. Your final tax liability is calculated when your taxable income, deductions, credits, filing status, investment income, spouse's income if applicable, and other tax items are assembled on your return.
Those two numbers do not have to match.
RSUs make the difference especially noticeable because a large vest can add tens or hundreds of thousands of dollars of wage income at once. Payroll may apply a supplemental-wage withholding method to that payment even though the extra income ultimately falls into a higher marginal federal income tax bracket.
For example, an employee might have federal income tax withheld at 22% on an RSU vest while some of the additional income ultimately falls into a 32%, 35%, or other applicable marginal bracket. The exact result depends on the employee's full-year return, not the RSU transaction in isolation.
How RSUs Are Taxed
A restricted stock unit is generally a promise by an employer to deliver stock or cash after specified conditions are satisfied. Unlike restricted stock that has already been transferred, an RSU normally does not give the employee actual stock at the grant date.
IRS guidance explains that RSUs generally are not taxable at grant when the applicable deferred-compensation requirements are satisfied. For typical stock-settled RSUs, income generally arises when the award vests and the stock is transferred to the employee. Source: IRS Publication 5992, Restricted Stock Units.
Suppose 500 shares settle when the company's stock is worth $200 per share. The compensation value is:
500 shares × $200 = $100,000 of compensation income.
That $100,000 is generally treated as wage income rather than capital-gain income at that point.
An important distinction from restricted stock is that an employee generally cannot make a Section 83(b) election for an RSU grant because no actual property has been transferred at grant. Source: IRS Publication 5992.
How Federal RSU Withholding Can Work in 2026
RSU compensation handled through payroll may be treated as supplemental wages for federal income tax withholding purposes.
For separately identified supplemental wages of $1 million or less during the calendar year, IRS rules can permit an employer to use an optional flat 22% federal income tax withholding rate when the applicable requirements are met. The employer may instead use an aggregate withholding method in qualifying circumstances. This means you should not assume every employer or every RSU vest automatically uses 22%. Source: IRS Publication 15 (2026), Supplemental Wages.
If an employee's supplemental wages from the employer exceed $1 million during the calendar year, the portion above $1 million is generally subject to mandatory federal income tax withholding at 37% for 2026. Source: IRS Publication 15 (2026).
Neither percentage is a promise that your final federal income tax on the RSU compensation will equal the amount withheld.
Payroll taxes are separate
Federal income tax withholding is only one part of the deduction you may see when RSUs settle.
Employee Social Security tax is generally 6.2% up to the annual Social Security wage base. For 2026, that wage base is $184,500. Medicare tax generally applies at 1.45% without a comparable wage ceiling. Source: IRS Topic No. 751 and Publication 15 (2026).
A 0.9% Additional Medicare Tax can also apply above filing-status-dependent thresholds. Employers, however, begin withholding the additional 0.9% after they pay an employee more than $200,000 of Medicare wages during the calendar year, regardless of the employee's filing status. The ultimate threshold is $250,000 for married filing jointly, $125,000 for married filing separately, and $200,000 for most other filers. Source: IRS Topic No. 560.
That is another example of why payroll withholding and final tax liability can diverge.
Worked Example: A $100,000 RSU Vest
Consider this deliberately simplified scenario. The figures are illustrative and are not intended to represent an average employee or a prediction of anyone's tax bill.
| Assumption | Amount |
|---|---|
| Shares settling | 500 |
| Share value at settlement | $200 |
| RSU compensation income | $100,000 |
| Illustrative federal withholding rate | 22% |
| Federal income tax withheld | $22,000 |
Now assume, solely for illustrating the withholding gap, that the employee's overall tax situation causes the incremental federal income tax associated with this additional $100,000 of income to work out to approximately 32%.
$100,000 × 32% = $32,000
Federal income tax withheld on the vest:
$100,000 × 22% = $22,000
Illustrative difference:
$32,000 − $22,000 = $10,000
The employee could therefore have an approximately $10,000 federal income-tax gap attributable to the assumptions in this example.
This is not a shortcut for preparing a tax return. Progressive tax brackets mean that different portions of income can be taxed at different rates, and deductions, credits, filing status, other compensation, investment income, and other factors can materially change the result.
The useful lesson is narrower: a 22% withholding calculation does not cap the tax ultimately attributable to the RSU income.
Other Reasons Your RSU Withholding and Final Tax Can Differ
1. Your salary already uses much of the lower tax brackets
A large RSU vest sits on top of salary, bonuses, commissions, and other taxable income. That additional compensation can therefore fall into higher marginal brackets than a flat supplemental withholding percentage might suggest.
2. You receive bonuses or several RSU vests
Looking at one vest in isolation can be misleading. Annual tax is based on the full year's income. Multiple vest dates, a cash bonus, a promotion, or a large year-end award can materially change the calculation.
3. Your spouse also earns substantial income
For married couples filing jointly, one employer generally does not know everything about the other spouse's compensation when withholding from a particular paycheck or equity award.
The combined return can therefore produce a different tax result from what either employer's payroll system appeared to anticipate.
4. State and local taxes follow different rules
State income-tax withholding rules are not uniform. The result can become more complicated if you worked in several states between grant and vesting, moved during the vesting period, or work remotely across state lines.
Employees in those situations should not assume the state shown on a current brokerage screen is the only jurisdiction potentially relevant to the award.
5. Additional Medicare Tax can create another reconciliation
The employer withholding trigger for Additional Medicare Tax is based on wages paid by that employer, while the individual's final liability depends on filing status and combined applicable income. Married couples can therefore encounter differences at filing time.
6. A later stock sale is a second tax event
The wage-income event and the eventual sale of the stock should be kept conceptually separate.
The value treated as compensation when the shares are received generally establishes an important part of your tax basis. A subsequent increase or decrease in the stock's value generally produces a capital gain or loss when the shares are sold.
A Practical RSU Withholding-Gap Check
You do not need to know your tax return to the penny months in advance. But you should have enough information to determine whether the amount being withheld is plausibly close.
- Estimate your full-year salary and other wage income. Include expected bonuses and other compensation.
- Add the expected taxable value of RSUs settling during the year. Remember that stock prices can move before the vest or settlement date.
- Estimate other material income. Examples include interest, dividends, business income, and realized capital gains.
- Estimate your total federal tax for the year. Use current-year rules rather than simply applying one tax bracket to every dollar.
- Compare that amount with expected withholding and credits. Include withholding from salary and equity compensation.
- Recalculate after a major vest. A large price movement or unexpected bonus can make an earlier estimate stale.
A simple preliminary formula is:
Estimated full-year federal tax − expected full-year withholding and credits = potential balance due.
That full-return approach is more useful than asking only, "How much tax was withheld from this vest?"
Should You Adjust Your W-4 or Make an Estimated Tax Payment?
If your projection shows a material shortfall, you may have more than one way to address it.
Employees can generally request additional federal income tax withholding from future paychecks through Step 4(c) of Form W-4. IRS Publication 505 specifically discusses using additional payroll withholding when existing withholding is expected to be insufficient. Source: IRS Publication 505 (2026).
Another possibility is making estimated tax payments.
For 2026, the general federal estimated-tax rule says estimated payments may be required if you expect to owe at least $1,000 after withholding and credits and your withholding and credits are expected to be less than the applicable required amount.
For many taxpayers, the commonly referenced safe-harbor comparison is the smaller of 90% of current-year tax or 100% of the prior year's tax. For certain higher-income taxpayers, 110% of prior-year tax replaces 100%. Special rules and exceptions apply. Source: IRS Publication 505 (2026) and IRS estimated-tax guidance.
| Approach | May be useful when | What to check |
|---|---|---|
| Increase W-4 withholding | You still have enough regular pay periods remaining | How much additional withholding is needed per paycheck |
| Estimated tax payment | A large vest or other income event creates a sizable projected gap | Payment timing and estimated-tax requirements |
| Set aside cash | You expect to owe at filing but are already within an applicable penalty safe harbor | Liquidity needed for the eventual payment |
| Professional tax projection | You have very large awards, several states, a spouse with substantial income, business income, or complex investments | Full federal and state return assumptions |
Avoid assuming that simply paying the balance with your tax return always resolves the issue. The U.S. federal system is pay-as-you-go, so insufficient payments during the year can sometimes lead to an underpayment penalty even when the full balance is eventually paid with the return. Source: IRS Topic No. 306 and Publication 505 (2026).
Do Not Forget the Stock Sale and Cost Basis
Once RSU shares have been delivered, a later sale is generally treated as a sale of a capital asset rather than another RSU wage event.
Suppose shares worth $200 each were included in compensation when received and you later sell them for $230 each. Subject to the applicable basis rules, the increase from the relevant basis to the sale price is generally the amount considered when calculating capital gain.
If you sell almost immediately after settlement, the capital gain or loss may be small because little time has passed for the stock price to move. It does not have to be exactly zero, however. Market movement and transaction details can create a gain or loss.
Pay particular attention to your Form 1099-B and equity-plan records. IRS broker-reporting rules for equity-based compensation can mean that the basis displayed on a brokerage tax document does not necessarily incorporate every compensation amount needed for your tax calculation.
Form 8949 is used when applicable to reconcile securities transactions and make permitted basis adjustments. Source: IRS Instructions for Form 8949 and Instructions for Form 1099-B.
This is important because an incorrect basis can make previously taxed compensation appear to be taxable again as capital gain.
What to Check After Every Major RSU Vest
- Confirm the number of units that vested and shares actually delivered.
- Record the fair market value used by payroll.
- Check the RSU income shown on the pay statement.
- Separate federal income tax withholding from Social Security, Medicare, state, and local withholding.
- Check whether the employer used a flat supplemental method or another payroll method.
- Update your estimate of total annual income and tax.
- Keep the vest statement, pay stub, and brokerage confirmation for later cost-basis reconciliation.
The Bottom Line
A large tax bill after an RSU year does not necessarily mean payroll made an error. It can simply mean that the amount withheld during vesting was lower than the tax ultimately calculated from your complete return.
The most common planning mistake is treating the withholding percentage as though it were the final tax rate. Instead, project salary, RSU compensation, bonuses, investment income, your spouse's income if filing jointly, deductions, credits, and expected withholding together.
If the projection shows a meaningful gap, consider increasing payroll withholding, making an appropriate estimated tax payment, or reserving additional cash after confirming the estimated-tax rules that apply to you.
This article is for general educational purposes and does not provide individualized tax, legal, or investment advice. Equity-compensation taxation can change materially based on award terms, settlement timing, filing status, state residency, work location, and other facts.
