---
title: "RSU Tax Withholding: Why 22% Is Never Enough (and What to Do About It)"
slug: rsu-tax-withholding
publishedAt: 2026-03-11T19:16:15.099Z
updatedAt: 2026-06-26T15:54:54.563Z
author: "Mike Navarro"
authorSlug: mike-navarro
category: "RSU Taxes"
tags: ["RSU", "Tax Withholding", "Supplemental Income", "W-4", "Sell to Cover"]
excerpt: "Your employer withholds 22% on RSU income, but your actual tax rate is 40-55%. Learn why the gap exists and 3 ways to avoid an April surprise."
canonical: https://myequitytax.com/blog/rsu-tax-withholding
---
RSU tax withholding happens at the flat 22% federal supplemental rate (37% above $1 million), but most tech employees fall in the 32-37% bracket, so the true rate is closer to 40-55%. Close the gap with W-4 changes, estimated payments, or a higher sell-to-cover percentage. This gap is the first of [the quiet leaks that show how much you're losing on equity comp](/blog/how-much-youre-losing).
Picture a typical case: a senior engineer has 2,000 RSUs vest worth $200,000. The broker sells shares to "cover taxes," the net deposit looks about right, and life moves on — until tax time eight months later brings a surprise five-figure bill that ten minutes of planning would have caught. That flat 22% line on the pay stub is one of the biggest sources of April surprises for equity-heavy employees.
This is the RSU withholding gap, and it catches even experienced engineers off guard.
## The RSU Tax Withholding Math
RSUs are classified as **supplemental income** by the IRS under IRC Section 3402(g). Your employer withholds at the flat supplemental rate ([IRS Publication 15](https://www.irs.gov/publications/p15)):
- **22%** on the first $1 million of supplemental income
- **37%** on supplemental income above $1 million
**Why 22%?** The IRS chose this rate as a rough middle-ground across all income levels. It matches the 22% tax bracket ($48,475-$103,350 for single filers in 2025) — but most tech employees earning RSUs are in the 32% or 35% bracket, making 22% woefully insufficient.
Your actual marginal tax rate — the rate applied to your last dollar of income — is almost certainly higher than 22%.
The chart below visualizes how the flat withholding rate compares to your true effective rate as RSU income climbs.
**If your total income is $250,000+**, your federal marginal rate is 32-37%. Add state tax and Medicare, and your true RSU tax rate is 40-55%.
**The shortfall is not a bug — it's by design.** The IRS requires employers to withhold at the 22% supplemental rate regardless of your actual bracket. It's your responsibility to make up the difference through estimated payments or W-4 adjustments.
## How Sell-to-Cover Works
When RSUs vest, most employers use "sell-to-cover" — see our deep-dive on [RSU sell to cover mechanics](/blog/rsu-sell-to-cover) for the full broker-side walkthrough:
1. All shares vest into your account
2. Broker immediately sells enough shares to cover withholding
3. Remaining shares stay in your account
**Example 1: $100K RSU vest at $250K salary (California)**
500 RSUs vest at $200/share ($100,000 value):
| Tax Component | Withheld | Rate |
|---------------|----------|------|
| Federal | $22,000 | 22% |
| State (CA) | $10,230 | 10.23% |
| Medicare | $1,450 | 1.45% |
| Additional Medicare | $900 | 0.9% |
| **Total withheld** | **$34,580** | **34.58%** |
| **Shares sold** | **173 shares** | |
| **Shares you keep** | **327 shares** | |
But your **actual tax liability** on this $100K at a $250K salary is closer to $47,000 — a **$12,420 shortfall** you'll owe when filing.
**Example 2: $50K RSU vest at $150K salary**
A more modest scenario, but the gap still bites. 250 RSUs vest at $200/share ($50,000 value):
| Tax Component | Withheld | Actual Tax (Incremental) |
|---------------|----------|-------------------------|
| Federal | $11,000 (22%) | $16,000 (32% marginal) |
| State (CA) | $5,115 (10.23%) | $4,650 (9.3% marginal) |
| Medicare | $725 (1.45%) | $725 (1.45%) |
| **Total** | **$16,840** | **$21,375** |
| **Shortfall** | | **$4,535** |
Even at $50K in RSUs, there's a $4,535 shortfall — driven almost entirely by the federal under-withholding. Notice that California's supplemental rate (10.23%) actually exceeds the marginal rate (9.3%) at this income level, providing a small state-level buffer.
## Complete Worked Example: $200K Salary + $100K RSU (California)
Here's the full tax walkthrough that shows exactly where the shortfall comes from:
This withheld total is what lands in Box 2 of your W-2 — see [how to read your RSU W-2](/blog/how-to-read-your-rsu-w-2) to reconcile it against your vests.
**Federal bracket walk-through (2025 rates, Single filer):**
- Total W-2 income: $300,000
- Standard deduction: $15,750
- Taxable income: $284,250
| Bracket | Income in Bracket | Tax |
|---------|------------------|-----|
| 10% | $11,925 | $1,193 |
| 12% | $36,550 | $4,386 |
| 22% | $54,875 | $12,073 |
| 24% | $93,950 | $22,548 |
| 32% | $53,225 | $17,032 |
| 35% | $33,725 | $11,804 |
| **Total federal tax** | | **$69,035** |
**RSU-attributable federal tax (incremental method):**
- Tax on $300K total income: $69,035
- Tax on $200K salary alone: $37,067
- RSU-attributable federal tax: **$31,968**
- Federal withheld on RSU (22%): $22,000
- **Federal shortfall: $9,968**
**State (CA) + Medicare:**
- CA tax on RSU (incremental): ~$9,300
- CA withheld on RSU (10.23%): $10,230
- CA surplus: ~$930 (over-withheld)
- Medicare + Additional Medicare: $2,350 (withheld correctly)
**Net shortfall: ~$9,968 - $930 = ~$9,038**
## The State Tax Surprise
State supplemental withholding rates often differ from actual marginal rates:
The comparison below shows how the gap between withholding and what you actually owe varies from state to state. The size of that gap depends heavily on where you live — see our state-by-state breakdowns for [California RSU vesting and withholding tax](/blog/ca-rsu-vesting-tax) and the [North Carolina RSU vesting tax rules](/blog/nc-rsu-vesting-tax) for two very different examples.
| State | Supplemental Withholding | Actual Top Marginal Rate | Gap |
|-------|--------------------------|-------------------------|-----|
| California | 10.23% | 13.3% (+ 1% mental health) | 3-4% |
| New York | 11.70% | 10.9% (+ NYC 3.876%) | -0.8% to +3% |
| Massachusetts | 5% flat | 9% (millionaire surtax) | 4% above $1M |
| New Jersey | none required | 10.75% | Full marginal rate |
| Oregon | 8% | 9.9% | 1.9% |
| Minnesota | 6.25% | 9.85% | 3.6% |
**Counterintuitive:** In some states like New York, the supplemental withholding rate (11.70%) actually *exceeds* the top marginal rate (10.9%) for many income levels, meaning you're over-withheld at the state level. However, NYC residents pay an additional 3.876% city tax that supplemental withholding does not cover, creating a net shortfall. Our [RSU Calculator](/calculator/rsu) accounts for this using the incremental tax method.
**NIIT alert:** If your adjusted gross income exceeds $200,000 (single) or $250,000 (married), you may also owe the 3.8% Net Investment Income Tax on investment income. While NIIT doesn't directly apply to RSU vesting (that's earned income), the extra W-2 income from RSUs can push your AGI above the NIIT threshold, making other investment income subject to the 3.8% surtax.
## 3 Ways to Close the RSU Tax Withholding Gap
Before you pick a fix, it helps to see the shortfall in dollars. Our free [RSU withholding shortfall calculator](/tools/rsu-withholding-shortfall) does it in seconds — enter your shares, salary, filing status, and state to see the exact gap between the flat 22% your employer withholds and your real marginal-bracket liability (plus the possible underpayment penalty). For a wider survey, see the [best RSU tax calculators in 2026](/blog/best-rsu-tax-calculators-2026) for tools that surface the withholding gap (and where each one falls short).
### 1. Adjust Your W-4 Withholding
The simplest approach: increase withholding on your regular paychecks to cover the RSU shortfall.
**How:** On [Form W-4](https://www.irs.gov/forms-pubs/about-form-w-4), Step 4(c), enter the additional dollar amount you want withheld per paycheck. Divide your expected annual shortfall by the number of remaining pay periods.
**Specific example:** You estimate a $12,000 annual shortfall. You have 24 semi-monthly pay periods remaining.
- W-4 Line 4(c): Enter **$500**
- That's $500 extra withheld per paycheck × 24 = $12,000 in additional withholding
The advantage of W-4 over estimated payments: paycheck withholding is treated by the IRS as if it were paid evenly throughout the year — even if you increase it in October. This means no underpayment penalty for earlier quarters.
### 2. Make Quarterly Estimated Payments
If your vesting events are large or irregular, quarterly estimated tax payments (Form 1040-ES) give you more control:
| Quarter | Due Date | Payment Method |
|---------|----------|---------------|
| Q1 | April 15, 2026 | IRS Direct Pay, EFTPS, or check |
| Q2 | June 15, 2026 | IRS Direct Pay, EFTPS, or check |
| Q3 | September 15, 2026 | IRS Direct Pay, EFTPS, or check |
| Q4 | January 15, 2027 | IRS Direct Pay, EFTPS, or check |
**State estimated payments** are separate: CA uses Form 540-ES (pay via CA Web Pay), NY uses Form IT-2105 (pay via NY Online Services). Other states have their own forms and rules — for example, our guide to [RSU vesting and withholding tax in Virginia](/blog/va-rsu-vesting-tax) walks through that state's flat-rate quirks.
For a complete walkthrough of when and how to make estimated payments on RSU income, see our [estimated tax guide for RSU income](/blog/estimated-taxes-on-rsu-income) and the [quarterly estimated tax guide for equity compensation](/blog/quarterly-estimated-tax-guide).
### 3. Increase Your Sell-to-Cover Percentage
Some brokers (Schwab, E*Trade, Morgan Stanley) let you specify a higher sell-to-cover percentage. Instead of the default, set it to your actual marginal rate:
| State | Recommended Sell-to-Cover % | Why |
|-------|---------------------------|-----|
| California | 52-55% | 35% federal + 9.3% CA + 1.45% Medicare + state surplus |
| New York (NYC) | 50-53% | 35% federal + 8.82% NY + 3.876% NYC + 1.45% Medicare |
| Texas / Washington | 40-42% | 35% federal + 0% state + 1.45% Medicare |
| Massachusetts | 45-48% | 35% federal + 5% MA + 4% surtax (>$1M) + 1.45% Medicare |
This eliminates the shortfall entirely — you just keep fewer shares. If you live in a no-income-tax state, your recommended sell-to-cover percentage is lower because there's no state withholding to account for — see how this plays out for [RSU vesting and withholding in Washington](/blog/wa-rsu-vesting-tax) and the parallel rules for [RSU vesting tax in Florida](/blog/fl-rsu-vesting-tax).
## Underpayment Penalty
If your shortfall exceeds $1,000 and you don't meet either IRS safe harbor (90% of current-year tax or 110% of prior-year tax), you'll owe an underpayment penalty ([Form 2210](https://www.irs.gov/forms-pubs/about-form-2210)). The penalty rate equals the federal short-term rate + 3 percentage points, adjusted quarterly (IRC Section 6654). In 2026, this rate is approximately 7-8%.
**Example:** $12,000 underpayment for the full year at 8% = ~$960 in penalties — on top of the $12,000 you already owe. The penalty is calculated per quarter, so paying late in Q4 doesn't fix the Q1-Q3 shortfall.
For a deeper dive on safe harbor rules and penalty calculations, see our [estimated tax guide for RSU income](/blog/estimated-taxes-on-rsu-income).
## If You Also Hold ISOs
Many tech employees hold both RSUs and ISOs. If that's you, RSU vesting events change your AMT-free exercise limit for ISOs — the extra W-2 income from RSUs shifts your tax brackets upward.
Planning RSU sales and ISO exercises together can save significantly more than optimizing each in isolation. For a complete understanding of how RSUs are taxed across both events (vesting and sale), see our guide on [how RSUs are taxed](/blog/how-are-rsus-taxed). For the bracket math behind all these calculations, reference the [2026 federal tax brackets](/blog/2026-federal-tax-brackets).
## Frequently Asked Questions
**Is RSU income subject to FICA?**
Yes. RSU vesting income is subject to Social Security tax (6.2% up to the $176,100 wage base in 2025), Medicare tax (1.45%), and Additional Medicare Tax (0.9% on income over $200,000). Your employer withholds these as part of sell-to-cover. If your salary alone exceeds the Social Security wage base, no additional Social Security tax applies to the RSU portion.
**Can I change my sell-to-cover percentage?**
It depends on your broker and employer plan. Schwab, E*Trade, and Morgan Stanley typically allow you to set a custom withholding rate through their equity compensation portals. Contact your company's stock plan administrator to check. Changes usually must be made before the vesting date.
**Do I need to make estimated tax payments on RSU income?**
If your withholding shortfall will cause you to owe more than $1,000 at tax time, and you don't meet either safe harbor rule, then yes. The simplest alternative is increasing your W-4 withholding, which avoids quarterly deadlines entirely.
**How is RSU income reported on my W-2?**
RSU vesting income is included in Box 1 (Wages) of your W-2 — combined with your salary, and treated as ordinary compensation income ([IRS Publication 525](https://www.irs.gov/publications/p525)). Most employers also show the RSU amount separately in Box 14 for reference, but this is informational only. The taxes withheld appear in Boxes 2 (federal), 4 (Social Security), 5 (Medicare), and 17 (state).
**What if I don't pay the shortfall?**
The shortfall doesn't go away — it becomes tax owed when you file your return. If you owe more than $1,000 beyond your withholding, the IRS charges an underpayment penalty (approximately 7-8% annually) calculated per quarter. You'll owe the tax plus penalty plus interest when you file.