Analysis by 
A California resident in the top federal bracket who vests $100,000 of restricted stock units keeps roughly $48,000 of it. The other $52,000 leaves in withholding before the shares ever settle in a brokerage account — and California claims a larger slice of that than most employees expect, because the state refuses to give equity income the favorable treatment the IRS reserves for long-term gains.
RSUs are taxed as ordinary income at vest: fair market value at the vest date multiplied by shares vested equals ordinary income, reported on the W-2. Nothing about that is California-specific. What makes California expensive is the stack: a 13.3% top state rate layered on top of a 37% federal rate, with no preferential capital gains rate to soften the state portion, applied to income that often arrives in a single concentrated event. This analysis breaks down where each dollar goes and calculates the RSU net yield after taxes for a California earner.
Scope: This article models California RSU taxation for the 2025 tax year using federal brackets from IRS Rev. Proc. 2024-40 and California rates from the 2025 FTB Tax Rate Schedules. All figures assume a resident employee taxed in California with W-2 RSU income. Marginal rate examples assume the employee’s other income already places them in the stated brackets; effective outcomes vary with total household income, filing status, deductions, and county of residence. This is a cost analysis, not tax or investment advice. State conformity rules and withholding mechanics change; verify current figures with the IRS and California Franchise Tax Board before acting on any vest.
The California RSU Tax Picture at a Glance
The headline numbers for a top-bracket California resident vesting RSUs in 2025:
| Figure | Value |
|---|---|
| Top federal ordinary income rate | 37% |
| Top California ordinary income rate (incl. 1% surcharge) | 13.3% |
| Medicare + Additional Medicare on RSU income | 2.35% |
| Combined marginal rate on RSU income (above SS wage base) | 52.65% |
| Finluxy Equity After-Tax Yield at top rates | 47.35% |
Sources: IRS Rev. Proc. 2024-40 (2025 federal brackets); California FTB 2025 Tax Rate Schedules; SSA 2025 wage base announcement. Combined marginal rate assumes income above the $176,100 Social Security wage base, so the 6.2% OASDI tax no longer applies.
Why California Hits RSUs Harder Than the Federal System Implies
California treats RSU income the same way it treats salary, and that is the entire problem. The state runs nine brackets from 1% to 12.3% for 2025, plus a 1% Behavioral Health Services Tax — the surcharge formerly known as the Mental Health Services Tax, renamed under Proposition 1 in 2024 — on taxable income above $1 million. That brings the top California rate to 13.3%, the highest state income tax rate in the country.
Here is the structural trap. Federal law gives long-term capital gains a preferential rate of 0%, 15%, or 20%. California does not. The Franchise Tax Board taxes capital gains as ordinary income at the same brackets as wages. For RSUs, this matters at two stages. At vest, the spread is ordinary income everywhere — federal and state. But even if an employee holds the shares afterward and qualifies for federal long-term capital gains treatment on subsequent appreciation, California still taxes that appreciation at up to 13.3%. The federal system rewards holding; California is indifferent to it.
Most coverage of equity compensation tax for high earners stops at the federal layer. The state layer is where California residents lose ground relative to employees in Texas, Washington, or Florida, who pay zero state tax on the identical vest.
Where Each Dollar Goes: A Component Breakdown
Consider an employee whose other compensation has already pushed them above the Social Security wage base and into the top federal and California brackets. A vest of 1,000 shares at an $85 fair market value produces $85,000 of ordinary income. The tax stack:
| Tax Component | Rate | Amount |
|---|---|---|
| Ordinary income at vest (FMV × shares) | — | $85,000 |
| Federal ordinary income tax | 37% | $31,450 |
| California ordinary income tax | 13.3% | $11,305 |
| Medicare + Additional Medicare | 2.35% | $1,998 |
| Total tax | 52.65% | $44,753 |
| Net after-tax proceeds | — | $40,247 |
| Finluxy Equity After-Tax Yield | — | 47.35% |
Sources: IRS Rev. Proc. 2024-40; California FTB 2025 Tax Rate Schedules; SSA 2025. Assumes income above the $176,100 Social Security wage base, so OASDI (6.2%) does not apply; Medicare runs 1.45% plus the 0.9% Additional Medicare surtax on wages above $200,000, for 2.35%. Figures are marginal — they apply to the RSU dollars stacked on top of existing income.
Note the FICA detail that trips up planning. If the RSU income arrives before the employee crosses the $176,100 Social Security wage base, an additional 6.2% OASDI applies to the portion below the cap, raising the marginal hit further on that slice. For most $150k+ earners receiving meaningful equity, salary alone clears the wage base, so the 6.2% is already exhausted and only the 2.35% Medicare component touches the RSU income. The 0.9% Additional Medicare surtax kicks in on wages above $200,000 — a threshold these employees clear easily.
The Withholding Gap That Creates April Surprises
Employers withhold federal tax on RSU income at the supplemental wage rate, not the employee’s actual marginal rate. The IRS flat supplemental rate is 22% for amounts up to $1 million in a calendar year, and 37% above that. California applies its own supplemental withholding rate to equity income, currently 10.23% for stock-based compensation.
For a top-bracket employee, 22% federal withholding against a 37% actual rate leaves a 15-percentage-point shortfall on every RSU dollar. On the $85,000 vest above, default federal withholding of $18,700 falls roughly $12,750 short of the $31,450 actually owed. California’s 10.23% supplemental withholding similarly undershoots the 13.3% true rate. The gap does not disappear — it surfaces as a balance due at filing, or as underpayment penalties if estimated taxes were not adjusted. This is the single most common reason high earners with equity owe large sums in April despite “full” withholding on their pay stub. The mechanics of timing these sales appear in any serious treatment of a 10b5-1 plan stock sale.
The Hold Decision: Why California Changes the Math
Once RSUs vest and tax is paid, the cost basis resets to the fair market value at vest. Subsequent gains or losses are capital gains measured from that basis. The classic vest-and-sell versus hold decision turns on whether expected appreciation justifies concentration risk and the tax drag on the gain.
For a California resident, the hold incentive is weaker than the federal numbers suggest. Hold shares more than a year and the federal rate on the gain drops to 20%, plus the 3.8% Net Investment Income Tax that applies above $250,000 of modified adjusted gross income for joint filers, or $200,000 for single filers — those thresholds are fixed by statute and not adjusted for inflation. But California taxes that same long-term gain at up to 13.3%, identical to the rate it charges on a short-term gain. The federal system offers a 17-point discount for patience; California offers nothing.
| Scenario | Federal Rate | CA Rate | NIIT | Total Tax | Finluxy Equity After-Tax Yield |
|---|---|---|---|---|---|
| Sell within 1 year (short-term) | 37% | 13.3% | 3.8% | $27,050 | 45.9% |
| Hold past 1 year (long-term) | 20% | 13.3% | 3.8% | $18,550 | 62.9% |
Sources: IRS Rev. Proc. 2024-40; California FTB 2025 Tax Rate Schedules; IRC §1411 (NIIT, threshold set in 2013 statute). Yield here is calculated on the $50,000 of appreciation only, not the underlying vested value. California’s 13.3% applies identically in both rows because the state does not distinguish short- from long-term gains.
The federal long-term holding period cuts the total tax on this appreciation from $27,050 to $18,550 — a real saving. But $13,300 of state tax sits in both columns, unchanged. A California resident weighing whether to hold is making a federal bet, not a federal-plus-state one, and the concentration risk of holding a single employer’s stock has to clear a lower tax hurdle to be worthwhile than it would in a no-tax state.
Finluxy Equity After-Tax Yield Across Scenarios
The Finluxy Equity After-Tax Yield expresses net after-tax proceeds as a percentage of pre-tax fair market value at the event date. The lower the yield, the more of the equity’s stated value evaporates in tax. California residents occupy the bottom of the range nationally.
| Scenario | Federal | State | FICA/Medicare | Finluxy Equity After-Tax Yield |
|---|---|---|---|---|
| RSU vest — California resident | 37% | 13.3% | 2.35% | 47.35% |
| RSU vest — no-income-tax state (e.g., TX, WA, FL) | 37% | 0% | 2.35% | 60.65% |
| RSU vest — California, income below SS wage base | 37% | 13.3% | 8.55% | 41.15% |
Sources: IRS Rev. Proc. 2024-40; California FTB 2025 Tax Rate Schedules; SSA 2025 wage base ($176,100). The third row adds the 6.2% OASDI tax for RSU dollars falling below the Social Security wage base, plus 2.35% Medicare, for 8.55% total payroll tax. Yield = (FMV − total taxes) ÷ FMV × 100.
The spread between the first two rows — 47.35% versus 60.65% — is the price of California residency on equity income: about 13 cents of every pre-tax RSU dollar, the full weight of the state rate. For an employee vesting $400,000 of RSUs in a year, that is roughly $53,000 in state tax that an identically paid colleague in Austin or Seattle simply does not owe.
What the Data Shows That Most Coverage Misses
The widely repeated figure is that California’s top rate is 13.3%, and employees brace for that number. The detail that gets lost: the 1% Behavioral Health Services surcharge only attaches above $1 million of taxable income. A $150k–$700k earner with a large vest is paying the 12.3% top regular rate, or one of the brackets below it, not the full 13.3% — unless a concentrated vest, an IPO event, or a bonus pushes total taxable income across the million-dollar line in a single year.
That makes the timing of large equity events a genuine lever. An employee who can spread vesting or sales across two tax years rather than bunching them may keep total taxable income under $1 million in each year and avoid the surcharge entirely on those dollars. The opposite is also true: an equity award at IPO that dumps several years of vesting into one taxable year can push an otherwise mid-bracket employee into surcharge territory and the top federal bracket simultaneously. The 13.3% number is not a fixed cost of being a California employee — it is a cost of crossing a specific threshold, and that threshold is plannable.
What This Means for a $150k+ California Household
At $150,000 of income, a single filer is in the 24% federal bracket and the 9.3% California bracket — not the top rates modeled above. A large RSU vest changes that. Stack $100,000 of RSU income on top of $150,000 of salary and the marginal dollars climb into the 32% or 35% federal bracket and the 10.3% or 11.3% California bracket, with the full 2.35% Medicare load because total wages clear $200,000. The Finluxy Equity After-Tax Yield for this household lands closer to 52–55% than to the 47% of the very top earner, but the structural lesson is identical: the state takes its cut at ordinary rates regardless.
Three decisions carry the most weight at this income level. First, withholding: the 22% federal supplemental rate almost certainly under-withholds against a marginal rate that the vest itself pushes higher, so quarterly estimated payments or additional W-4 withholding prevent an April shortfall and underpayment penalties. Second, the $1 million surcharge line: households approaching it through a combination of salary, bonus, and equity should know that crossing it adds 1% to every dollar of taxable income above the line, and that spreading equity events across tax years can keep dollars below it. Third, the hold-versus-sell call: because California erases the federal long-term capital gains advantage on its own portion, holding concentrated employer stock has to be justified almost entirely on the federal rate differential and on conviction about the stock — not on a state tax benefit that does not exist. For households comparing option strategies, the same state-level indifference shapes the ISO versus NSO tax cost and the 83(b) election tax analysis, where California’s refusal to grant preferential rates compounds every federal decision.
Methodology
Federal ordinary income brackets and long-term capital gains thresholds come from IRS Rev. Proc. 2024-40 for the 2025 tax year. California rates and the nine-bracket schedule come from the 2025 Franchise Tax Board Tax Rate Schedules; the 1% surcharge above $1 million is the Behavioral Health Services Tax, formerly the Mental Health Services Tax under Proposition 63 and renamed under Proposition 1 (2024). Payroll tax figures — the $176,100 Social Security wage base, 1.45% Medicare, and 0.9% Additional Medicare surtax above $200,000 — come from the Social Security Administration’s 2025 announcement and IRS guidance. The 3.8% Net Investment Income Tax threshold is set by IRC §1411 statute and is not inflation-indexed.
RSU taxation follows the framework in IRS Publication 525: fair market value at vest multiplied by shares vested equals ordinary income, with cost basis resetting to that value for subsequent capital gains measurement. The Finluxy Equity After-Tax Yield is calculated as net after-tax proceeds divided by pre-tax fair market value at the event date, times 100. All scenarios are marginal — they model RSU dollars stacked on top of an employee’s existing income at the stated brackets, not blended effective rates across an entire return. I verified each rate and threshold against current primary sources before modeling, because California’s non-conformity to several federal provisions makes secondary summaries unreliable for state figures. Where a household’s actual outcome depends on filing status, total income, and county of residence, the article reports marginal rates and notes that effective results will differ.
Frequently Asked Questions
Does California tax RSUs differently from salary?
No. California taxes RSU income at vest as ordinary income, using the same nine-bracket schedule it applies to wages. There is no preferential rate for equity compensation at the state level, which is precisely why the state portion of an RSU tax bill is so large relative to the federal portion for those who hold and qualify for federal long-term capital gains treatment.
Why did I owe so much California tax in April despite withholding at vest?
California withholds on RSU income at a 10.23% supplemental rate, and the federal supplemental rate is 22% for amounts up to $1 million. For a top-bracket employee facing 37% federal and 13.3% California marginal rates, both withholding rates fall short of the actual liability. The difference becomes a balance due at filing unless estimated payments were increased during the year.
Does holding RSU shares for over a year help in California?
Holding helps federally — the long-term capital gains rate drops to 20% from the 37% short-term rate on post-vest appreciation. It does not help at the state level. California taxes long-term and short-term capital gains identically, at up to 13.3%. The hold decision for a California resident rests on the federal rate differential and concentration risk, not on any state tax benefit.
When does the extra 1% California surcharge apply to my RSUs?
The 1% Behavioral Health Services Tax applies to taxable income above $1 million, for all filing statuses. RSU income counts toward that total. A large vest, an IPO, or bunched equity events can push an otherwise mid-bracket household across the line, at which point every taxable dollar above $1 million carries the extra 1%. Spreading equity events across tax years can keep income below the threshold.
Sources & References
- IRS Publication 525 — Taxable and Nontaxable Income, equity compensation sections
- IRS Rev. Proc. 2024-40 — 2025 federal tax brackets and inflation adjustments
- California Franchise Tax Board — 2025 Tax Rate Schedules
- Social Security Administration — 2025 Contribution and Benefit Base ($176,100)
- IRS — Additional Medicare Tax (0.9% over $200,000)
- IRS Topic 559 — Net Investment Income Tax (IRC §1411, 3.8%)
- IRS Form 3921 and supplemental wage withholding guidance