RSU Tax in California (2026): Rate Stack, Withholding Gap, and FTB Rules for Bay Area Tech Employees

The California RSU tax stack: federal + 13.3% state + MHST + NIIT

RSU vest-day income is wages. For a California resident in the federal top bracket, the all-in marginal rate on the next vested dollar lands close to 51%: 37% federal ordinary income, plus 0.9% Additional Medicare Tax on wages above threshold under IRC Section 3101(b)(2), plus 13.3% California state income tax under California Revenue and Taxation Code Section 17041(a)(1). The 13.3% headline stacks the 12.3% top marginal under Section 17041(a)(1) and the 1% Mental Health Services Tax under Section 17043 on taxable income above $1 million.

Two additional CA components show up on the wage side. The state’s State Disability Insurance assessment under SB 951 became uncapped in 2024 and applies to wages without a ceiling — high-earner RSU vests pay it on every additional dollar of compensation per the EDD’s annual contribution rate notice. Second, capital-gain income on subsequent share appreciation is taxed at the same ordinary 13.3% top rate under Section 17041; California has no preferential long-term capital-gain rate. The federal 3.8% Net Investment Income Tax under IRC Section 1411 lands on top of post-vest gains for high-AGI households. That rate stack makes California the tightest jurisdiction in the country for unhedged RSU concentration.

The supplemental withholding gap, California edition

Federal withholding on RSU vesting defaults to 22% under IRC Section 3402(g) (37% above $1 million of cumulative supplemental wages). The California analogue, the EDD’s stock-options-and-bonus supplemental rate, is 10.23% per the EDD’s Publication DE 44, California Employer’s Guide. Both rates are below the marginal rate most Bay Area RSU recipients owe.

For a Staff Engineer in the federal 37% bracket and the California 13.3% top bracket, the vest-day withholding is structurally short by approximately 15 percentage points federal and 3 percentage points state — about 18 cents on every dollar of RSU vest income, before any AMT or NIIT layering. On a $250,000 NVDA vest, that is roughly $45,000 of underpayment that does not exist on the W-2 by April 15. Quarterly estimated payments per IRS Publication 505 federal and the FTB’s parallel Form 540-ES schedule state. See the withholding-gap explainer for the integrated estimated-payment template.

Trailing nexus: why California still taxes you after you move to Texas

California asserts the right to tax RSU vest-day income for the portion of the grant-to-vest period during which the employee performed services in California — even after the employee has moved to a no-tax state. The position is laid out in FTB Publication 1004, Stock Option Guidelines, FTB Publication 1100, Taxation of Nonresidents and Individuals Who Change Residency, and the FTB Residency and Sourcing Technical Manual, and was bound to a specific RSU fact pattern in FTB Chief Counsel Ruling 2013-02.

In practice, an engineer who receives a four-year RSU grant while living in San Francisco and moves to Austin halfway through the vesting period continues to owe California state tax on the California-workday share of every remaining vest until the grant fully vests. The 2024 California OTA ruling reaffirmed the position and is documented in practitioner analyses including State and Local Tax Blog’s 2024 OTA writeup. A move out of California closes the door on new days; it does not erase the days already worked.

The mechanic is the workday-allocation formula: California source income equals the vest-day W-2 figure times the ratio of California workdays to total workdays during the grant-to-vest period, computed grant-by-grant. Multi-state travel, remote-work days, and PTO all enter the denominator; the FTB Residency and Sourcing Technical Manual treats business-travel days, vacation days, and weekends as non-California where the employee is physically not present in the state.

Worked example: $250K NVDA vest in San Francisco

Illustrative scenario. A Senior Software Engineer at Nvidia has a $250,000 RSU vest on a quarterly tranche, all California-sourced (no out-of-state workdays during the grant-to-vest period). Federal supplemental withholding at 22%: $55,000. California stock-supplemental withholding at 10.23%: $25,575. FICA capped at the wage base, plus 1.45% Medicare and 0.9% Additional Medicare on wages above threshold: roughly $5,500 combined. Net deposit to brokerage after withholding: roughly $164,000.

Actual federal liability at the 37% top bracket: $92,500. Federal underwithholding: $37,500. Actual California liability at the 13.3% top bracket (assuming the engineer has $1M+ of total state taxable income with the MHST threshold crossed): $33,250. California underwithholding: $7,675. Combined April surprise on this one vest: roughly $45,000. The number gets worse when stacked with three other quarterly vests of similar size and the Q4 vest hitting after the cumulative supplemental wage total crosses $1 million federal — at which point the federal supplemental rate jumps to 37% and the gap closes, but the prior three vests have already locked in the 22% withholding shortfall.

Worked example: $500K META vest, principal engineer

Illustrative scenario. A Principal Engineer at Meta vests $500,000 in a single semi-annual tranche, again all California-sourced. By this vest the engineer has already crossed the $1 million federal cumulative supplemental wage threshold, so the federal supplemental rate on the entire $500,000 is 37%: $185,000. California supplemental at 10.23%: $51,150. Net deposit after withholding (before payroll’s sell-to-cover mechanics): roughly $245,000 on a $500,000 gross vest.

Federal liability is approximately even — 37% withholding matches the marginal bracket, with a small 0.9% Additional Medicare gap. California liability at 13.3% on the full vest: $66,500. Underwithholding state-side: $15,350. The MHST is embedded in the 13.3% calculation; the engineer crossed the $1M MHST threshold long before this vest. NIIT under Section 1411 layers onto any subsequent post-vest capital gain, which is why holding the META shares and selling them eighteen months later compounds the all-in marginal rate up toward 53% combined federal-plus-state on the appreciation slice.

A sell-to-cover mechanic that zeros the federal supplemental gap does not zero the California gap. A high-earner Bay Area household with multiple equity events in a single year owes the FTB a meaningful estimated payment whether the federal side balances or not.

What Proposition 30 was — and why there is no $2M surcharge

Tax content circulating online occasionally references a Proposition 30 surcharge of 1.75% on California personal income above $2 million. That surcharge does not exist. Proposition 30, on the November 2022 California ballot, proposed to fund electric-vehicle and wildfire-prevention programs by adding a 1.75% personal-income tax on income above $2 million. Voters rejected it, with roughly 59% of the vote against. The measure is a matter of public record on the California Secretary of State’s 2022 election results page and the California Legislative Analyst’s Office Proposition 30 analysis.

Why the myth persists: the structurally identical 1.75% surcharge was also part of an earlier 2018 ballot measure that did not pass, and the 1% Mental Health Services Tax of Proposition 63 (2004) is a real surcharge on income above $1 million that lives in the 13.3% top bracket today. Tax content that conflates the three produces a phantom “13.3% + 1.75% Prop 30 = 15.05%” rate that nobody pays. California’s top combined rate on RSU income for 2026 remains 13.3% under Section 17041, plus the SB 951 SDI contribution on the wage side and the federal stack on top of that.

Bay Area company-specific: Meta, Google, Apple, Nvidia withholding behavior

All four large Bay Area employers default to the federal 22% supplemental rate on RSU vest withholding through the year until cumulative supplemental wages cross $1 million per IRC Section 3402(g), then switch to 37%. State-side, all four use the EDD’s 10.23% stock-supplemental rate. None of them withhold at the employee’s actual marginal rate by default; the gap is structural across the entire FAANG cohort and drives the surprise April 15 liability most Bay Area engineers encounter.

Two employer-specific patterns matter for high-earner Bay Area households. First, several large employers offer a W-4 override that lets engineers elect a higher fixed supplemental withholding rate per-vest — workable when available, but rarely advertised by payroll. Second, Apple and Google in particular vest semi-annually rather than quarterly, which concentrates the under-withholding into two large April-15 surprises rather than four smaller ones; Meta and Nvidia vest quarterly. Estimated-tax payment timing should match the vesting cadence on the actual employer plan, not a generic quarterly schedule.

Strategies for high-income California residents

Three levers consistently move the California RSU bill. First, donor-advised-fund gifting of long-term appreciated post-vest shares: the IRC Section 170(b) charitable deduction reduces both federal and California taxable income, and California fully conforms to Section 170 on charitable contributions. A Bay Area household bunching two or three years of charitable intent into a single high-vest year routinely saves $30,000+ in combined federal-plus-state tax on the gifted shares alone.

Second, deduction bunching coordinated with the SALT cap. California’s 13.3% rate amplifies the value of any deductible event that lives in a single year — the post-2018 SALT cap means the state-tax deduction is largely lost on W-2-only Bay Area households, but pass-through-entity tax elections (PTE under California AB 150) do flow through and recover most of the federal SALT deduction for households with qualifying business income.

Third, concentrated-position deferral via Section 351 exchange-fund conversion. For employees with $250K+ of low-basis vested-and-held RSU concentration, a Section 351 ETF-conversion structure swaps the single-stock position for a diversified fund without triggering the immediate capital-gains recognition that would otherwise hit at the 13.3% California rate plus 23.8% federal LTCG-plus-NIIT — the Section 351 ETF-conversion structure page covers the mechanics. Direct indexing with tax-loss harvesting can also generate state-side losses against vesting RSU gains; California fully conforms to federal capital-loss rules on this front.

Moving to Texas or Washington: the right and wrong way

A pre-IPO or pre-large-vest move from California to a no-income-tax state can be one of the highest-dollar planning moves in a tech career, but it has to be executed against the FTB’s actual sourcing rules — not the popular-press version. Wrong way: move January 1, vest April 1, assume the vest is all Texas-source. The grant-to-vest workday formula in FTB CCR 2013-02 sources the vest based on where the work to earn it was performed, and the prior three years of California workdays still allocate to California.

Right way: model the grant-by-grant California percentage before the move, document workday counts contemporaneously, and sequence sales of post-vest shares to the years after bona-fide nonresidency is fully established. The FTB applies a multi-factor residency test under FTB Publication 1031 — primary home, voter registration, vehicle registration, family location, time spent — and treats no single factor as dispositive. Federal-court and OTA case history shows the FTB pursues suspect departures hard. Practitioner analyses including the National Law Review’s OTA writeup document the pattern.

A move executed two or three years before a known liquidity event, with documented out-of-state workdays for the entire pre-event window, is defensible. A move executed one to three months before a vest or sale is not.

Run the California numbers on your own grant

The California RSU calculation is mechanical once you have vest-day FMV, your federal bracket, your CA marginal rate, and an estimate of California-workday percentage on each outstanding grant. Apply the federal-plus-CA rate stack to a candidate vest; the full RSU tax guide covers the multi-state mechanics in depth, and the concentrated-stock playbook is where Bay Area households with $500K+ of single-employer exposure should start. Above that threshold the California rate stack makes the diversification calculus tighter than almost any other jurisdiction in the country; grant-level planning across the full vesting tail changes the outcome in ways a single-vest optimization does not.

Book a 30-minute fiduciary consultation