California RSU tax calculator (2026)
RSU vesting in California: 22% federal supplemental + 10.23% California stock supplemental + FICA + SDI. Combined withholding ~41%. The withholding gap can hit 10-15 percentage points for high earners, plan estimated quarterly payments.
Equity compensation tax is fact-specific and high-stakes. This page summarises 2026 published guidance from IRS Publication 15 (federal supplemental rates), the California EDD DE 4 (state supplemental rates), and the California FTB. RSUs, ISOs, NQSOs, ESPPs, and double-trigger structures all behave differently. Consult a CPA or financial planner specialising in California tech equity before making decisions on large vesting events, sales, or charitable strategies.
How RSU vesting is taxed in California
On the day a Restricted Stock Unit (RSU) vests, the fair-market value of the vested shares is treated as ordinary wage income for both federal and California state purposes. The employer is required to withhold federal income tax, California state income tax, Social Security, Medicare, and SDI at supplemental rates. The employer typically uses sell-to-cover (liquidating a portion of the vested shares to fund the withholding) before depositing the remaining shares in the worker's brokerage account. The full vested value is reported on the worker's W-2 in Box 1 (wages) and the corresponding withholding amounts in Box 2 (federal income tax withheld) and Box 17 (state income tax withheld).
The mandatory federal supplemental withholding rate is 22% on cumulative supplemental wages up to $1 million per recipient per calendar year, and 37% on the portion above $1 million (per IRS Publication 15). California uses a higher supplemental rate for stock options and similar equity-vesting events: 10.23% (per the EDD DE 4 withholding instructions). This is meaningfully higher than the 6.6% rate that California uses for cash bonuses, California recognises that equity vesting events tend to involve high-marginal-rate workers. FICA applies: 6.2% Social Security on wages up to the $176,100 cap (per the SSA October 2025 COLA notice), 1.45% Medicare on all wages with no cap. Additional Medicare 0.9% applies to total wages above $200,000 (single) or $250,000 (MFJ household). SDI at 1.1% applies to all California wages with no cap (per January 2024 SB 951).
The withholding gap: worked examples by California tech band
For workers in the federal 22% bracket and California 9.3% bracket, the supplemental withholding (22% + 10.23%) closely matches actual tax owed. For workers in higher federal brackets (24%, 32%, 35%, 37%), the 22% federal supplemental under-collects, creating a year-end shortfall. Below shows the gap at common California tech compensation tiers, assuming the worker has taxable income from regular salary that places them in the indicated marginal brackets when the RSU vest is added.
| Scenario | RSU value | Withheld at vest | Net at vest | Actual tax owed | Year-end gap |
|---|---|---|---|---|---|
| Mid-tech ($150k base + $50k vest) Fed 22%, CA 9.3% | $50,000 | $20,490 | $29,510 | $20,025 | $465 refund |
| Senior tech ($180k base + $100k vest) Fed 24%, CA 9.3% | $100,000 | $40,980 | $59,020 | $42,050 | $1,070 owed |
| Senior+ ($250k base + $200k vest) Fed 32%, CA 9.3% | $200,000 | $81,960 | $118,040 | $100,100 | $18,140 owed |
| Staff/principal ($400k + $500k vest) Fed 35%, CA 10.3% | $500,000 | $204,900 | $295,100 | $270,250 | $65,350 owed |
Approximations only. Actual gap depends on the worker's full annual taxable income, filing status, deductions, AMT exposure (for ISOs), and whether the worker is also subject to the 3.8% Net Investment Income Tax on capital gains from later share sales. The pattern is clear: for high earners the federal 22% supplemental rate routinely under-collects.
Double-trigger RSUs: the IPO / acquisition tax bomb
Most California pre-IPO startup RSUs use a double-trigger vesting structure. Two conditions must both be satisfied for the RSUs to vest: (1) time-based service vesting (typically 4-year vesting with a 1-year cliff), AND (2) a liquidity event (IPO, SPAC merger, acquisition, or secondary tender offer). Under the double-trigger structure, no taxable event happens at the time-based vest if the liquidity event has not yet occurred. The shares are simply tracked as time-vested but not yet released.
When the liquidity event happens, all the cumulative time-vested shares hit at once as taxable wages on the vest date. For an early-stage employee with 4 years of accumulated time-vested RSUs at IPO, this can produce a single supplemental wage event of $500,000 to $5 million or more, depending on company size and the worker's grant. The federal supplemental withholding applies the 22% rate to the first $1 million and 37% to the rest. This routinely produces an under-collection vs the worker's actual marginal rate (often 32% to 37% federal), leaving a year-end balance owed in the hundreds of thousands of dollars. Combined with California's 9.3% to 13.3% state rate, total tax owed at IPO frequently exceeds 50% of the vest value. Pre-IPO planning with a CPA familiar with California tech equity is essential.
Strategies sometimes used: charitable contribution of appreciated shares (donor-advised fund or 501(c)(3) direct), rule 10b5-1 trading plans for orderly post-IPO sales, AMT planning if any portion is ISO-style, qualified small business stock (QSBS) exclusion under IRC 1202 if eligibility tests are met (potential federal exclusion of up to $10 million or 10x basis on certain pre-2018 grants, California does not conform to QSBS, so 100% of the gain remains California-taxable). Each of these has detailed eligibility tests; consult a CPA with California pre-IPO equity experience.
Mitigating the RSU tax shortfall
Three practical approaches for California workers facing an RSU tax shortfall after a vesting event. First, increase regular W-4 / DE 4 withholding via the "additional withholding" line for the remainder of the year. This is administratively simple and produces no penalty risk. The downside: cash flow comes from each remaining paycheck rather than from a one-time payment. Second, make quarterly estimated tax payments via IRS Form 1040-ES (federal) and FTB Form 540-ES (California). The quarterly deadlines are April 15, June 15, September 15, and January 15 of the following year. Third, make a year-end estimated payment to bring total withholding plus estimates above the safe-harbor threshold (the lower of 90% of current-year tax OR 110% of prior-year tax for AGI above $150,000) to avoid the IRS underpayment penalty.
For very-high-earner California tech workers facing six-figure RSU shortfalls, working with a fee-only CFP and a CPA familiar with California equity comp is typically worth the cost. Mistakes at this income level (missing AMT exposure on ISOs, mistiming charitable donations, failing to elect QSBS where eligible) easily run into six-figure tax differences. The full strategy menu and cross-link to other California tax mechanics is on the increase take-home pay and bonus tax pages.
Related California paycheck pages
California RSU tax, common questions
RSU tax mechanics on this page reflect 2026 published rates from IRS Publication 15 (federal supplemental withholding), California EDD DE 4 (state supplemental withholding), and the SSA October 2025 COLA notice (Social Security wage base). California does not conform to federal QSBS (Qualified Small Business Stock) exclusion under IRC 1202. ISOs trigger AMT exposure separate from regular income tax. Double-trigger vesting structures, ESPP qualifying dispositions, and sec 83(b) elections each have additional fact-specific rules. Consult a CPA or financial planner specialising in California tech equity for advice on your circumstances.