RSU Withholding Calculator: What Federal Rate Should You Choose at Each Vest?

When an RSU vest hits, most payroll systems withhold federal income tax at a flat 22%. That number has nothing to do with your tax rate. It is a payroll convention the IRS makes available to employers, and for a household earning enough to receive meaningful equity, it is usually too low.

The question worth answering is this one: given everything already withheld this year, every paycheck still to come, and every vest still ahead of me, what rate should I elect on the next one? It has two defensible answers, and they can be twenty percentage points apart. Both are derived below from the 2026 brackets and the IRS safe-harbor rules, and the calculator solves them from your numbers.

What actually happens at vest

When an RSU vests and the shares are delivered, their fair market value becomes ordinary compensation income in that year. It stacks on top of your salary and counts for federal income tax, state income tax, Social Security, Medicare, and Additional Medicare. Your employer typically sells or holds back a portion of the shares to cover withholding and delivers the rest.¹

The IRS treats RSUs as unfunded promises to deliver stock later, which is why the taxable event waits for vesting rather than grant. It is also why RSUs do not qualify for a Section 83(b) election. The IRS audit guide for equity compensation states it directly: RSUs are “not considered property for purposes of IRC § 83 since no actual property has been transferred, and therefore an IRC § 83(b) election cannot be made with respect to the grant of a Restricted Stock Unit.”²

Why 22%, and what your employer is allowed to do

RSU income is a supplemental wage. For supplemental wages up to $1 million in a calendar year, IRS Publication 15 gives employers two methods. They can use the aggregate method, combining the vest with regular wages and withholding as though it were all one paycheck. Or they can use the optional flat-rate method, which is where 22% comes from. Under that method the rate is fixed: employers may “withhold a flat 22% (no other percentage allowed).”³

One prerequisite gets left out of nearly every explanation: the flat-rate method is only available if the employer withheld income tax from that employee’s regular wages in the current or immediately preceding calendar year. A new hire whose first payroll event is an RSU vest cannot be withheld under the flat method at all.³

As for why the rate is 22% and not something else, the IRS says so plainly in the 2026 Employer’s Tax Guide: the supplemental rate “remains 22% (37% if supplemental wages paid to an employee during the calendar year exceed $1 million) because P.L. 119-21 permanently extended the individual tax rates enacted in P.L. 115-97.” The One Big Beautiful Bill Act made the seven-rate structure permanent, and 22% is the flat rate pinned to it.³ It is an administrative simplification, not an estimate of anyone’s liability. It knows nothing about your filing status, your spouse’s income, your deductions, or how much of the lower brackets your salary has already consumed.

Above $1 million the rate is no longer optional. Cumulative supplemental wages beyond that point are withheld at 37% “without regard to the employee’s Form W-4,” and the threshold counts payments from all businesses under common control, not just one payroll system.³

What your plan actually lets you elect

The IRS sets the flat-method rate. Your employer sets the menu. These are different things, and conflating them is the most common error in RSU content. Three real plan designs, each documented in SEC filings:

• The employer sets the amount; you choose only the method. This is the most common design, and the language is close to boilerplate across filed equity plans. A representative agreement gives the company discretion over the amount withheld, which “may, in the discretion of the Administrator, be in excess of the minimum statutory required amount to be withheld,” then confines the employee to an enumerated menu: paying cash, having shares held back (“Net Share Withholding”), or “Sell to Cover.” Elect nothing and a default applies. In that plan, “Net Share Withholding will be the method by which such Withholding Obligations are satisfied.”⁴ Worth noting that the discretion runs upward as well: a plan can withhold above the statutory minimum without you electing anything.
• A binary 22% or 37% toggle, sometimes irrevocable. Live Oak Bancshares filed its election letter as an exhibit to its annual report: “instead of withholding at a 22% rate, the Company will withhold at the maximum applicable federal income tax rate (currently 37%)... for Section 16 officers who sign and return this letter.” Note both limits. It is offered only to Section 16 officers, and signing it “irrevocably” directs the higher rate.⁵
• Any whole percentage inside an employer-defined band. An InfoSpace election form let employees add “an additional ___% (please insert a number from 1 to 10; the total tax withholding cannot exceed 35%)” on top of the statutory minimum. The filing is from 2007, when the supplemental rate was 25%, so it illustrates the structure rather than current numbers.⁶

Fidelity, which administers a large share of these plans, puts the general rule this way: “Your company may let you choose how to withhold taxes on your award, or it may have a mandatory default method of withholding. Check your plan documents on NetBenefits for details of the available tax withholding methods, including any decision windows and how to estimate your tax withholding.”⁷

So before running any numbers, find out which of those worlds you live in, and whether there is a deadline. Some plans lock the election weeks before the vest date.

Your top bracket overstates the rate on the vest

A common piece of advice is to elect your marginal bracket. That is directionally sensible and usually close, but it overshoots, because a vest is not taxed entirely at your top rate. It fills the remaining room in your current bracket first, then spills upward.

Take a single filer with a $200,000 salary and $100,000 of RSUs vesting during the year. Total wages of $300,000 less the 2026 standard deduction of $16,100 gives $283,900 of taxable income, which does reach the 35% bracket. But the vest itself spans three brackets. Without it, taxable income is $183,900, sitting in the 24% band. The vest therefore runs through the tail of 24%, all of 32%, and into 35%:⁸

The top bracket is 35%. The rate that actually applies to the vest is 31.4%. Withholding at 22% covers $22,000 of a $31,400 bill, leaving a $9,400 federal shortfall on this vest alone, before state tax or Additional Medicare. Electing 35% would overshoot by $3,600 in the other direction.

The effect is smaller but still real at lower incomes. A married couple with $180,000 of taxable income before a $120,000 vest is in the 24% bracket at the top, but $31,400 of that vest still falls in the 22% band before the rest crosses into 24%. The blended rate is 23.48%, the incremental tax is $28,172, and the gap at 22% withholding is $1,772. Close enough that 24% is a fine election here. The calculator reports the blended figure rather than the top bracket, which is why its recommendation sometimes lands a notch below what you would guess.

Two targets, two different rates

Withholding does not change what you owe. It changes when you pay it. Your liability is set by your full-year income and filing status; the refund or balance at filing is just the difference between that number and what was sent in during the year. So the election is a cash-flow decision with a penalty constraint attached, and there are two sensible places to aim.

Both are the same calculation with a different target plugged in:

“All other projected payments” means federal tax already withheld this year, withholding expected from the rest of your paychecks and your spouse’s, and any estimated payments already made. “Remaining RSU income” is this vest plus every vest left in the year.

The full-liability target is your entire projected federal tax. Hit it and you owe roughly nothing in April. The safe-harbor target is the smaller of 90% of this year’s tax or 100% of last year’s total tax, rising to 110% of last year’s if your prior-year AGI was above $150,000 ($75,000 if married filing separately). Last year’s return has to cover all twelve months.⁹ Hit that and you avoid the underpayment penalty, which is not at all the same as owing nothing.

A worked example where the two answers diverge

Assume a household with:

• Projected 2026 federal tax of $88,000
• Prior-year total tax of $60,000, with prior-year AGI above $150,000
• $42,000 of expected withholding from salary
• $14,000 already withheld on earlier vests
• $100,000 of RSU value left to vest this year

Other projected payments come to $42,000 plus $14,000, or $56,000. The full-liability rate is straightforward:

The safe-harbor target is the smaller of 90% of $88,000 ($79,200) and 110% of $60,000 ($66,000), so $66,000. That gives:

Ten percent is below the minimum any plan offers. So electing the 22% floor already clears safe harbor with room to spare: $56,000 plus $22,000 is $78,000 against a $66,000 threshold. No penalty. And this household would still owe roughly $10,000 at filing.

That is the distinction almost every RSU explainer collapses. Safe harbor governs whether you owe a penalty; it says nothing about the size of your April bill. Deciding between 10% and 32% here is a genuine choice: 22% keeps roughly $10,000 of liquidity through the year at the cost of needing it available in April, while 32% removes the decision at the cost of an interest-free loan to the Treasury.

When 22% already overshoots the full bill

The gap can also run the other way, and this is the case that catches people who reason “I’m in the 24% bracket, so I should elect 24%.” Take a married couple filing jointly with $250,000 of projected federal taxable wages between them and one $80,000 vest left in the year. Total wages of $330,000 less the $32,200 standard deduction gives $297,800 of taxable income and a projected federal tax of $56,668.⁸ Without the vest, taxable income would be $217,800, which already sits inside the 24% band. So this vest, unlike the one in the blended-rate example above, really is taxed at 24% dollar for dollar: it adds exactly $19,200 of tax.

Even so, 24% is not the rate to elect. Suppose withholding from the couple’s regular paychecks projects to $42,000 for the year, which happens easily when one spouse’s W-4 is still set to the single table. The full-liability equation gives:

The solved rate sits below the 22% floor, so any election the plan offers overshoots:

At 22% this household is already over-withheld against its full liability. Moving the election to 24% to match the bracket does nothing except add $1,600 to the interest-free loan. The blended-rate section above showed that the bracket usually overstates the tax on the vest itself; this example shows that even when it does not, the election is answering a household question. Payroll withholding that runs ahead of the salary’s share of the bill absorbs part of the vest’s tax, and payroll that runs behind leaves the vest to cover more than its own. The solved rate can land above the menu, inside it, or below it, and only the equation tells you which household you are.

The calculator

Enter your filing status, YTD wages and withholding, the vest you’re deciding on, and the rates your plan offers. It solves both targets, models Social Security and Medicare against the vest date, checks safe harbor, and if your highest available rate still falls short, computes the per-paycheck W-4 amount that closes the gap.

Why the timing of withholding beats the timing of a payment

This is the part with the largest practical payoff and the least coverage anywhere else.

The federal system is pay-as-you-go, and the underpayment penalty is computed per quarter. Miss the first-quarter installment and interest accrues from that date, even if you overpay later. That is why a December estimated payment cannot undo a Q1 shortfall.

Wage withholding works differently. The instructions to Form 2210 say that “for withheld federal income tax and excess social security or tier 1 RRTA, you are considered to have paid one-fourth of these amounts on each payment due date unless you can show otherwise.”¹⁰ The same rule sits in the statute at IRC § 6654(g)(1).

Dollars withheld from a December RSU vest are therefore treated as though a quarter of them arrived back in April. Raising your election on a late-year vest can retroactively cure an underpayment from earlier in the year in a way that writing a check in January cannot. If you discover in November that you have been under-withheld all year, the vest election and the W-4 are the better instruments.

Two cautions. The even-quarters treatment is the default, not something you opt into, and the burden runs the other way: a taxpayer who wants the actual withholding dates used instead must show them and check box D on Form 2210. And this reduces or eliminates a penalty; it does not reduce the tax.

For scale, the penalty is interest, not a flat fee, and the rate is reset quarterly. For individuals it was 7% for the first quarter of 2026, 6% for the second, and 7% for the third.¹¹ On a $10,000 shortfall carried a few months, that comes to a few hundred dollars at most. Worth avoiding when it is free to avoid, and not worth reorganizing your finances around.

Social Security, Medicare, and the two-earner trap

Federal income tax is the biggest piece, but payroll taxes shift the answer at the margin, and they shift by vest date. For 2026:

• Social Security is 6.2% up to a $184,500 wage base, then stops.¹² A January vest on a $200,000 salary burns through the cap quickly; by late summer, additional vests carry no Social Security tax at all. Maximum employee Social Security tax for 2026 is $11,439.
• Medicare is 1.45% on all wages, with no cap.
• Additional Medicare Tax is 0.9% on wages above $250,000 for joint filers, $200,000 for single and head of household, and $125,000 for married filing separately.¹³

The Additional Medicare rules create a predictable mismatch. An employer must start withholding the 0.9% once it pays an employee more than $200,000, “without regard to the individual’s filing status or wages paid by another employer.”¹³ So a married couple each earning $150,000 has $300,000 of combined wages and zero withheld, because neither employer individually crosses $200,000. At filing they owe 0.9% on the $50,000 above the joint threshold, or $450, that nobody collected. The IRS answer is to make estimated payments or request additional withholding on Form W-4. A higher RSU election absorbs it just as well.

The reverse happens if you changed jobs mid-year. Each employer applies a fresh $184,500 Social Security wage base, so someone who switched companies during a heavy vesting year is likely over-withheld on Social Security. That money is not lost; it comes back as a credit on your return. But it means your total withholding is already running ahead of where a naive projection would put it.

When the plan menu is too coarse

There are two knobs, and they are good at different things:

1. The vest election. Changes withholding only on future vests, in whatever increments your plan allows.
2. Form W-4, Step 4(c). The line is titled “Extra withholding” and takes a dollar amount per pay period.¹⁴ It applies to every remaining paycheck and is adjustable at any time.

If your plan offers a rate near your solved number, use the election. If the jumps are coarse, which is common when the only choices are 22% and 37%, the election alone will always overshoot or undershoot. Elect the lower rate and close the remainder with Step 4(c), which lets you tune by dollar rather than by a fifteen-point step. Divide the gap by your remaining paychecks. The calculator prints this figure.

Estimated quarterly payments are the fallback when neither knob is available, for example when the shortfall comes from income no employer touches. Given the Form 2210 timing rule above, prefer withholding when you have the choice.

When not to bother changing your election

There are real cases where the default is fine and the optimization is noise:

• Your safe-harbor rate is already below the plan minimum. As in the worked example above, this happens whenever last year’s tax was much lower than this year’s. You are penalty-safe at 22%. The only question left is whether you would rather hold the cash or hand it over early, and there is no wrong answer as long as the money is actually there in April.
• Cash flow is comfortable and you value simplicity. If you keep a large buffer and are in the habit of paying a balance at filing, leaving the vest at 22% is defensible. The penalty is interest at single digits, not a fine.
• You will harvest losses that offset the vest. Up to $3,000 of net capital loss offsets ordinary income per year, and realized losses offset realized gains without limit, so a December harvest can lower the full-year picture enough that 22% lands close.
• Your supplemental wages will pass $1 million this year. Everything above the breakpoint withholds at a mandatory 37% no matter what you elect, and that alone often more than covers the gap on the earlier vests.³

Why the default sticks, and why that is worth ten minutes

The strongest reason to spend time on this is that almost nobody does, and the reason is inertia rather than a considered judgment.

Damon Jones studied how households respond when their tax liability changes and found that prepayments adjust by only 29% of the change after a year, and 61% after three years. His conclusion was that “policies affecting default-withholding rules are no longer neutral decisions.”¹⁵ Defaults in payroll settings are famously sticky in general: under 401(k) automatic enrollment, Madrian and Shea found roughly three-quarters of participants sitting at the default contribution rate.¹⁶

There is also a case that deliberate over-withholding is not simply irrational. Naomi Feldman studied the 1992 change to withholding tables, which moved refund dollars into monthly paychecks without changing anyone ’s tax, and found it reduced the probability that households contributed to a tax-preferred retirement account, consistent with treating a refund as a distinct pot of money.¹⁷ If you know you would spend the extra liquidity rather than reserve it, aiming at full liability is a reasonable commitment device even though it costs you the interest.

Worth being honest about the limits here: there is no academic research on supplemental-wage withholding elections specifically. This literature is adjacent, and it supports a modest claim, which is that the 22% default persists because changing it requires work, not because it fits.

Withholding is not your diversification plan

Electing a higher rate means more shares sold at vest, which incidentally trims your company-stock position. Do not let that stand in for an actual portfolio decision. Receiving vested RSUs is economically the same as receiving cash and immediately choosing to buy your employer’s stock, and the two decisions have different inputs.

FINRA puts the concentration problem directly: “In the event your company falters, not only might your investments tumble, but you might also find yourself out of work at the same time.” The same page points to a 10% cap on any single stock, including your employer’s, as a figure some advisers use, while noting it may still be too high depending on your circumstances.¹⁸ Lisa Meulbroek estimated the cost of ignoring this: an employee holding company stock equal to a quarter of total wealth over a ten-year horizon gives up roughly 42% of that stock’s market value to risk that diversification would have removed at no cost in expected return.¹⁹ That figure moves with the assumptions, reaching 52% at a fifteen-year horizon and falling to 27% when company stock is one-eighth of wealth.

Set withholding to fund your tax bill. Decide separately whether the remaining shares belong in your portfolio.

When to bring in a professional

Everything above assumes a US employee with public-company RSUs and a reasonably ordinary tax picture. Get advice if any of these apply:

• Supplemental wages approaching or above $1 million. The IRS withholding estimator itself declines these, warning that if you “expect to earn $1 million or more in bonuses” it “can’t calculate your withholding accurately.”²⁰
• Private-company double-trigger RSUs, or a Section 83(i) deferral
• A mid-year move between states, or work in multiple states
• ISOs in the same year, where AMT interacts with everything else
• Large or unpredictable capital gains, business income, or K-1 income
• Any non-US tax residency or treaty question

Frequently asked questions

Is 22% my RSU tax rate?

No. It is a withholding rate, and only one of the methods an employer may use. Your actual tax on the vest depends on your full-year income and filing status. For most households receiving meaningful equity, the real rate on the vest is higher than 22%.

Can I change my RSU withholding rate?

It depends entirely on your employer’s plan, and you will see confident claims in both directions online. Some plans set the rate for you and offer only a choice of method. Some offer a 22% or 37% toggle, occasionally irrevocable and occasionally restricted to executives. Some allow any whole percentage in a range. The IRS fixes the rate under the flat method; everything above that is plan design. Check your plan documents.

What if my plan only offers 22%?

Use Form W-4, Step 4(c). Take the gap between your projected tax and projected withholding, divide by the number of paychecks left in the year, and enter that dollar figure. The calculator computes it. A W-4 change usually takes effect within one or two pay cycles.

Should I aim for safe harbor or for zero balance due?

Safe harbor if you have the liquidity to pay a balance in April and would rather hold the cash, and if you will genuinely reserve it rather than spend it. Full liability if your income is unpredictable, you dislike filing-time surprises, or you know the money will not survive until April. They optimize for different things, so the choice turns on your cash position and your habits rather than on tax rules.

Do I still need estimated quarterly payments?

Only if you cannot close the gap through withholding. Because withholding is treated as paid evenly across the year while estimated payments are dated, a W-4 or vest-election change is the better tool whenever you have the option, particularly late in the year.

Should I change my RSU withholding to match my tax bracket?

Not as a rule. The election’s job is to close the gap between your projected payments and your target, and your bracket is only one input to that gap. A household whose vest is taxed at 24% can correctly elect 22% when payroll withholding is running ahead of the rest of the bill, and can need 32% or more when it is running behind. Solve the equation, or let the calculator do it, before touching the election.

Why did more than 22% of my shares get sold at vest?

Because federal income tax is only one of the taxes the shares cover. Share withholding also funds Social Security at 6.2% until the $184,500 wage base is filled, Medicare at 1.45%, Additional Medicare at 0.9% once your employer has paid you over $200,000, and state income tax where it applies, and brokers round up to a whole share. A total share haircut in the low 30s is routine even when the federal income-tax election is exactly 22%. Read the vest confirmation’s breakdown by tax type before concluding your election was applied incorrectly.

Does the vest date matter?

Yes, in two ways. A vest early in the year is more likely to be subject to Social Security tax, since the $184,500 wage base may not be filled yet. And an early vest leaves many paychecks over which to correct any misjudgment through the W-4, while a December vest leaves almost none.

Does any of this apply outside the US?

No. This is US federal tax only. RSU treatment varies by country and by residency status within a country. If you vested while working abroad, talk to a cross-border specialist.

Key takeaways

• 22% is a payroll convention. It is the optional flat-rate method for supplemental wages, fixed at 22% by statute because the OBBBA made the seven-rate structure permanent. It is not calibrated to anyone’s liability.
• Solve for the rate, do not guess at it. Required rate equals your payment target minus all other projected payments, divided by remaining RSU income.
• Compute it twice. Once against safe harbor and once against full liability. The two answers are frequently far apart, and choosing between them is a liquidity decision.
• Safe harbor is a penalty rule. Clearing it says nothing about the size of your April bill.
• Your top bracket overstates the rate on the vest. The vest fills the rest of your current bracket before spilling upward, so the blended rate is lower.
• Late-year withholding is unusually powerful. It is deemed paid in equal quarterly installments, so it can cure an earlier underpayment that a Q4 estimated payment cannot.
• Keep the tax decision separate from the portfolio decision. Set withholding to fund the bill, then decide independently whether to hold the shares.

Related guides

• Sell Your RSUs at Vest for the portfolio half of the decision, once withholding is settled.
• The RSU Bridge Strategy for running household cash flow when vest proceeds are your main liquidity source.
• RSU Tax Strategy for the sell-versus-hold question and cost basis after the vest.
• Concentration Risk for measuring single-stock exposure and building a multi-year diversification plan.
• Human Capital Risk for Tech Workers for why your employer is already your largest undiversified asset.
• Tax-Loss Harvesting for offsetting the capital-gains side once you start selling.
• Roth vs. Traditional 401(k) because your marginal rate drives both decisions.

Sources and method

1. Morgan Stanley. Restricted Stock Unit Basics For U.S. Employees. Ordinary compensation at vest and delivery, subject to withholding.
2. IRS. Publication 5992, Equity (Stock)-Based Compensation Audit Techniques Guide. Taxable event at vesting; Section 83(b) unavailable for RSUs.
3. IRS. Publication 15 (2026), Circular E, Employer’s Tax Guide, section 7. Flat 22% with no other percentage allowed, the regular-wages prerequisite, the $1 million breakpoint and 37% rate, and the OBBBA explanation in What’s New.
4. Harmonic Inc. 2025 Equity Incentive Plan, Restricted Stock Unit Agreement (Exhibit 4.2 to Form S-8), section 7(b). Company-determined withholding amount, an enumerated method menu, and a net-share-withholding default. The same clause appears in many other filed plans, for example NetApp’s 2021 Equity Incentive Plan RSU agreement.
5. Live Oak Bancshares. Exhibit 10.6.9 to the FY2023 Form 10-K. Irrevocable 37% election for Section 16 officers.
6. InfoSpace. Form of Restricted Stock Unit Award Tax Withholding Election Form (EX-10.34, 2007). Employee-selected increment within an employer-defined ceiling. Cited for plan structure; the 2007 rates are obsolete.
7. Fidelity Investments. Stock plan services: a guide to taxes and tax filing. Withholding methods are determined by the company.
8. IRS. Revenue Procedure 2025-32, sections 4.01 and 4.14. 2026 bracket thresholds and standard deductions, reflecting P.L. 119-21.
9. IRS. Publication 505 (2026), Tax Withholding and Estimated Tax. The 90%/100% general rule, the 110% higher-income substitution, and the twelve-month prior-return requirement. See also Topic 306 for the under-$1,000 penalty exception.
10. IRS. Instructions for Form 2210 (2025), Part III, line 11. Withholding deemed paid in four equal installments. Statutory basis at IRC § 6654(g)(1). The 2025 revision is the current one; a 2026 edition publishes in early 2027.
11. IRS. Quarterly interest rates. Noncorporate underpayment rate of 7% for Q1 2026, 6% for Q2, and 7% for Q3 (Rev. Rul. 2026-10, I.R.B. 2026-22). Reset each quarter.
12. IRS. Topic no. 751, Social Security and Medicare withholding rates. 2026 wage base of $184,500. Confirmed in Publication 15 (2026).
13. IRS. Questions and answers for the Additional Medicare Tax. Filing-status thresholds, the $200,000 per-employer withholding trigger, and the two-job shortfall scenario.
14. IRS. Form W-4 (2026), Step 4(c). “Enter any additional tax you want withheld each pay period.”
15. Damon Jones (2012). Inertia and Overwithholding: Explaining the Prevalence of Income Tax Refunds. American Economic Journal: Economic Policy 4(1), 158-185.
16. Brigitte C. Madrian and Dennis F. Shea (2001). The Power of Suggestion: Inertia in 401(k) Participation and Savings Behavior. Quarterly Journal of Economics 116(4), 1149-1187.
17. Naomi E. Feldman (2010). Mental Accounting Effects of Income Tax Shifting. Review of Economics and Statistics 92(1), 70-86.
18. FINRA. Love Your Company Stock? Here’s What to Know, August 2023. Concentration risk and the 10% guideline.
19. Lisa K. Meulbroek (2005). Company Stock in Pension Plans: How Costly Is It? Journal of Law and Economics 48(2), 443-474. Value-loss estimates vary with the share of wealth held and the holding period.
20. IRS. Tax Withholding Estimator. The $1 million bonus limitation appears in an in-application help note on the income step.
21. Method: bracket arithmetic in this guide was computed from the Revenue Procedure 2025-32 tables and cross-checked against the printed “The Tax Is” column at every threshold. The single-filer example assumes the standard deduction and no other income; the married example works from taxable income directly. Dollar figures are rounded to the nearest dollar.