RSU Tax Withholding: Why the 22% Default Leaves You Owing in April
Your employer withheld 22% on that RSU vest. Your actual marginal federal rate is 32%. Nobody told you, the pay stub looked fine, and in April you owe $6,000 you didn’t budget for. This is the single most common surprise in equity compensation, and it isn’t a payroll error — RSU tax withholding follows a flat supplemental-wage rule that has nothing to do with your real bracket.
This guide shows exactly how the gap forms, a five-step calculation to size yours before year-end, a worked example at a $180,000 salary with a $60,000 vest, and the four ways to close it without triggering an underpayment penalty.
Who Gets Burned by RSU Tax Withholding, and Who Doesn’t
When restricted stock units vest, the full market value on the vest date becomes ordinary W-2 income. Your employer has to withhold something, and most of them use the optional flat rate for supplemental wages. Per IRS Publication 15 (Circular E) for 2026, that rate is 22% on supplemental wages up to $1 million in a calendar year, and a mandatory 37% on anything above $1 million.
Notice what’s missing from that rule: you. The 22% is not an estimate of your tax situation. It’s a default that happens to be exactly right for people whose marginal bracket is 22% and progressively wrong for everyone above it.
So the honest answer to “does this affect me” comes down to one number. Using the 2026 brackets from Revenue Procedure 2025-32, the 22% bracket tops out at $105,700 of taxable income for single filers and $211,400 for married couples filing jointly (Tax Foundation, 2026 brackets). Below those lines, flat withholding is roughly correct and you can stop reading. Above them, every dollar of vested stock is under-withheld — by 2 points in the 24% bracket, 10 points in the 32% bracket, and 15 points at the top.
Two groups get hit hardest. Engineers and managers at public tech companies, where RSUs routinely make up 20 to 40 percent of total compensation. And anyone whose grant appreciated sharply between grant and vest, because the tax is on vest-date value, not on what the company promised you in the offer letter.
What You Need Before You Run the Numbers
Three inputs, all of which you already have access to.
1. Your vesting schedule with estimated values. Pull it from your equity portal. You need the number of units vesting in the current calendar year and a reasonable price assumption. Use today’s price — forecasting your own stock is a separate mistake.
2. Your latest pay stub, showing year-to-date federal withholding and year-to-date gross. The stub also tells you how your employer handles the vest: “sell to cover” (shares sold automatically to fund withholding) or “net settlement” (shares withheld). Either way, the 22% question is identical.
3. Last year’s Form 1040, line 24 (total tax) and line 11 (AGI). These drive the safe harbor calculation in Step 5 and determine whether you owe a penalty or merely a balance.
Five Steps to Size Your RSU Tax Withholding Gap
Step 1 — Add up total 2026 vest value. Units vesting this calendar year multiplied by current share price. Include vests that already happened; the gap is cumulative across the year, not per-event.
Step 2 — Find your real marginal bracket including the RSU income. Take total wages plus vest value, subtract the 2026 standard deduction ($16,100 single, $32,200 married filing jointly) or your itemized total, and locate the result in the bracket table. Use the bracket the top of your income lands in, not the average.
Step 3 — Multiply the vest value by the difference between that bracket and 22%. A $60,000 vest at a 32% marginal rate under-withholds by 10 points, or $6,000. This is the rough version and it’s usually within a few hundred dollars of the exact answer.
Step 4 — Add state tax if your state has an income tax and your employer flat-rated that too. Many do, using a state supplemental rate that is similarly disconnected from your actual liability. This is also where high earners should check the 0.9% Additional Medicare Tax on wages above $200,000 — usually withheld correctly by a single employer, frequently missed if you changed jobs mid-year.
Step 5 — Compare against the safe harbor, not against zero. You do not have to pay in 100% of what you’ll owe to avoid a penalty. You need the lesser of 90% of this year’s tax or 100% of last year’s total tax — 110% if your prior-year AGI exceeded $150,000. That threshold matters enormously for people with large vests, and we work through the choice in detail in our breakdown of the 100% vs. 90% estimated tax safe harbor. Miss it and the IRS charges interest on the shortfall: the underpayment rate for individuals is 7% for the third quarter of 2026 — the federal short-term rate plus three percentage points, compounded daily (Internal Revenue Bulletin 2026-22).
A Worked Example: $180,000 Salary, $60,000 Vest
Single filer, no other income, standard deduction. Salary $180,000, RSUs vesting at $60,000 during 2026.
Total income is $240,000. Subtract the $16,100 standard deduction and taxable income is $223,900 — which lands in the 32% bracket, since the 2026 single-filer 32% band runs from $201,776 to $256,225.
The RSU income is the last $60,000 stacked on top, so it straddles two brackets:
- $163,900 to $201,775 — $37,875 taxed at 24% = $9,090
- $201,776 to $223,900 — $22,125 taxed at 32% = $7,080
- Federal tax actually attributable to the vest: $16,170
Withheld at the flat rate: $60,000 × 22% = $13,200. The shortfall is $2,970, and the effective federal rate on that vest was 27%, not 22%. Add a state with a 5% income tax that also flat-rated the vest at a lower supplemental rate, and the April number grows again.
Here’s the general version. This table assumes the entire vest sits in one bracket, which slightly overstates the gap for people straddling a boundary — like the example above — but it’s the right mental model:
| Your marginal federal bracket | Withheld per $10,000 vested | Actually owed | Gap per $10,000 | Gap on a $60,000 vest |
|---|---|---|---|---|
| 22% | $2,200 | $2,200 | $0 | $0 |
| 24% | $2,200 | $2,400 | $200 | $1,200 |
| 32% | $2,200 | $3,200 | $1,000 | $6,000 |
| 35% | $2,200 | $3,500 | $1,300 | $7,800 |
| 37% | $2,200 | $3,700 | $1,500 | $9,000 |
Federal only. State income tax, where applicable, stacks on top.
Four Ways to Close the Gap Before April
1. Ask payroll to raise your ongoing withholding. The cleanest fix. Submit a new Form W-4 with an extra amount on the “additional withholding” line, sized to cover the gap across the remaining pay periods. Withholding is treated as paid evenly throughout the year regardless of when it actually happened, which means a December adjustment can retroactively cure a shortfall created by a March vest. Estimated payments do not get that treatment.
2. Make a quarterly estimated payment. Works, but timing matters — an estimated payment is credited when made, so a Q4 payment does not fix a Q1 underpayment. If you’re using this route, pay in the quarter the vest occurred.
3. Sell some of the vested shares to fund the bill. There’s no tax cost to selling immediately at vest, because your cost basis equals the vest-date value you already paid ordinary income tax on. A same-day sale produces roughly zero capital gain. If the stock has since dropped and you’d be selling at a loss, check the timing rules first — the same 30-day repurchase trap that catches index fund investors applies here, and our wash sale rule case study walks through how it bites.
4. Offset with a deliberate loss elsewhere in the portfolio. Capital losses offset capital gains and up to $3,000 of ordinary income per year, so this is a partial lever at best against a large vest — but if you’re already sitting on losers, harvesting them in the same year costs nothing extra. The tradeoff between harvesting losses now and resetting basis higher is covered in our comparison of tax gain harvesting versus tax loss harvesting.
Wondering what the after-tax proceeds are worth if you diversify them instead of holding company stock?
Common Mistakes That Turn a Gap Into a Penalty
Assuming the pay stub means it’s handled. The withholding line is accurate — it’s the rate that’s wrong. Nothing on the stub flags a mismatch with your bracket, and payroll has no obligation to tell you.
Thinking the tax bill drops if the stock falls. It does not. The ordinary income is locked at vest-date value. If the price halves afterward, you owe tax on the higher number and hold a capital loss you can only deduct $3,000 of per year against ordinary income. This is the scenario that has genuinely wrecked people.
Holding vested shares because selling “feels like a loss.” The endowment effect is doing the talking here, not analysis. A vested RSU is a cash bonus that arrived in the form of stock, and holding it is a decision to buy your employer’s stock with that cash. Most people would not make that purchase deliberately — especially given that their salary, health insurance, and future vests already depend on the same company. If concentration risk is the concern, the case for a broad-market position instead is laid out in our comparison of total stock market versus S&P 500 index funds.
Putting the proceeds in the wrong account. Once you’ve diversified, where the replacement holdings live changes your after-tax return meaningfully over a decade — the logic is in our guide to asset location and where to hold bonds.
Waiting until you file. The gap is knowable in January from your vesting schedule. Discovering it in April means you’ve lost every cheap fix and are left with the expensive one.
What the Fixed Version Looks Like
Sized correctly, this stops being an event. In January you total the year’s scheduled vests, apply the bracket difference, divide by remaining pay periods, and put that number on a W-4. Each vest then either gets sold same-day into a diversified fund or held deliberately with a written reason. April becomes arithmetic instead of a surprise.
The broader point: RSU tax withholding is one of the few personal finance problems where the default is not merely suboptimal but structurally wrong for the exact population most likely to receive it. The system isn’t going to fix that. Ten minutes with a vesting schedule and a bracket table will.
A Note From Chris
I’m a software engineer, so I’ve had the flat-rate conversation with more than one colleague who assumed payroll had done the thinking for them. What surprised me is how much of the resistance isn’t about the tax at all — it’s about selling. People who cheerfully dollar-cost-average into index funds will hold a single-company position representing a third of their net worth and describe it as “letting it ride.” I run my own money without an advisor, mostly in index funds across tax-advantaged accounts, and my rule is that anything arriving as company stock gets treated as a cash bonus that happens to be denominated in shares. Automate the sale, automate the reinvestment, remove the decision.
The behavioral economics literature has a tidy name for the reluctance — we own it, therefore we value it more than we’d pay for it — and knowing the name doesn’t make it go away. What works is deciding the rule before the vest date, when nothing is at stake, and then not renegotiating with yourself in the moment. That’s the same pre-commitment logic that makes automated retirement contributions work, applied to a much larger and much lumpier number.
Key Takeaways
- Employers withhold a flat 22% on supplemental wages up to $1 million (37% above), per IRS Publication 15. That rate is unrelated to your actual bracket.
- In 2026 the 22% bracket ends at $105,700 of taxable income for single filers and $211,400 for joint filers. Above those lines, every vested dollar is under-withheld.
- A $60,000 vest at a 32% marginal rate under-withholds by roughly $6,000 federal, before state tax.
- You only need to hit the safe harbor — 90% of this year’s tax or 100% of last year’s (110% if prior-year AGI topped $150,000) — not the full liability.
- Extra W-4 withholding is treated as paid evenly across the year, so a December adjustment can cure a shortfall from a March vest. Estimated payments cannot.
- The underpayment interest rate for individuals is 7% for Q3 2026, compounded daily.
- Selling at vest has near-zero capital gains cost, because basis equals the vest-date value you were already taxed on.
