RSU Vesting at California Termination — 10.23% Withholding + Broker Mechanics

Who this applies to#

This scenario applies to a California employee — most commonly a tech-sector individual contributor or manager at a public or late-stage-private company — whose RSU grant produces a vesting event on or around the termination date. The mechanism varies: sometimes the severance agreement includes an accelerated vest clause that lifts the service condition on otherwise unvested tranches; sometimes a scheduled vest date falls on the last day of employment or in the trailing days under a garden-leave or salary-continuation structure; sometimes a quarterly vest cadence happens to coincide with a layoff announcement. The common element is that shares actually settle in the plan account, the fair market value at settlement enters payroll as ordinary wages, and a withholding event hits the same paycheck cycle as any final salary or severance components. The assumed profile for this walk-through is a senior IC earning $220,000 in base salary at a California-headquartered company, laid off without cause mid-year, with $300,000 in unvested RSUs at the grant level. The severance agreement accelerates a single tranche worth $200,000 at the vest-date fair market value; the remaining $100,000 of unvested grant forfeits under the standard plan terms. The accelerated vest produces ordinary income at settlement, the broker runs a default sell-to-cover transaction to fund withholding, and the employee retains the post-tax remainder in shares. Most of the scenario's editorial weight is on what the W-2 reports, what the 1099-B reports, and how the two interact at filing time — because that interaction is the single most common source of employee tax errors on equity compensation. The scenario does not cover stock options (ISOs or NSOs), ESPP, or performance-vesting units in depth — each has its own settlement and basis rules and is treated in a dedicated scenario. The narrow focus here is on standard time-vesting RSUs that settle as shares in the year of termination, where the California 10.23% supplemental rate applies as the bonus/stock rate under EDD DE 231PS rather than the 6.6% rate that governs cash severance. The walk-through is descriptive and regulatory; it does not recommend a hold-versus-sell strategy or a state-residency change.

What changes for you#

The federal income-tax treatment of an RSU settlement is established by 26 U.S.C. § 83 and the regulations under it. Under § 83(a), the fair market value of property transferred in connection with the performance of services is included in the service provider's gross income at the first time the rights are transferable or no longer subject to a substantial risk of forfeiture, less any amount paid for the property. For a standard time-vesting RSU with no purchase price, that means the FMV at vest is wage income on the vest date. IRS Publication 525 walks through the mechanics in plain language and is the public-facing companion to § 83. The income enters payroll, the employer issues a W-2 reporting the inclusion in Box 1, and federal supplemental withholding applies under IRS Pub 15 § 7. The 2026 IRS Pub 15 specifies: "The withholding rate on supplemental wages remains 22% (37% if supplemental wages paid to an employee during the calendar year exceed $1 million) because P.L. 119-21 permanently extended the individual tax rates enacted in P.L. 115-97." On a $200,000 accelerated vest, the federal supplemental component is $200,000 × 22% = $44,000, assuming the employee is not over the $1M cumulative threshold for the year. The California-side treatment is where the rate distinction matters. EDD Publication DE 231PS, "Personal Income Tax Withholding — Supplemental Wage Payments, Moving Expense Reimbursement — WARN Act Payments," is explicit on the two-tier California flat rate: "For stock options and bonuses that were paid on or after November 1, 2009, the flat rate is 10.23 percent. For other types of supplemental wage payments made on or after November 1, 2009, the flat rate is 6.6 percent." RSU settlements are stock for this purpose — the vest delivers shares — and the 10.23% rate applies. On a $200,000 RSU vest, California supplemental withholding is $200,000 × 10.23% = $20,460. This is meaningfully higher than the 6.6% rate that applies to cash severance: an employee whose final paycheck combines $50,000 of cash severance and a $200,000 RSU vest will see two separate California supplemental lines on the stub, and the two-tier split is correct per DE 231PS, not a payroll error. The statutory basis for the employer's withholding obligation is Cal. Unemp. Ins. Code § 13020, which requires every employer to withhold PIT on wages paid to a resident or nonresident performing services in California. FICA continues to apply on RSU settlements the same as on cash wages. OASDI at 6.2% on the employee side runs up to the 2026 Social Security wage base of $184,500 published by SSA. A senior IC at $220,000 base salary will typically have crossed the OASDI wage base on a regular paycheck before a mid-year termination, so the marginal OASDI withholding on the RSU vest is often zero. Medicare at 1.45% applies to the full $200,000 with no cap, producing $2,900. The additional 0.9% Medicare surtax under 26 U.S.C. § 3101(b)(2) kicks in once cumulative Medicare wages cross $200,000 single or $250,000 MFJ; an employer begins withholding the surtax once the individual employee's YTD Medicare wages with that employer cross $200,000, so the surtax very commonly applies on a senior-IC accelerated vest, producing roughly $1,800 of additional Medicare withholding on a $200,000 vest if the threshold has already been crossed for the year. CA SDI is the California-specific always-on layer: SB 951 eliminated the SDI taxable-wage cap effective January 1, 2024, and the EDD Rates page specifies: "The SDI withholding rate for 2026 is 1.3 percent." On $200,000 of RSU income, that is $2,600 of SDI regardless of YTD wages, because the cap is gone. The total withholding stack on a $200,000 accelerated RSU vest, assuming the OASDI wage base has already been crossed and the additional Medicare surtax is active, is: $44,000 federal supplemental + $20,460 CA supplemental + $0 OASDI + $2,900 base Medicare + $1,800 additional Medicare + $2,600 CA SDI = $71,760. At the vest-date FMV, the broker sells roughly $71,760 of shares to fund the withholding remittance, and the employee retains shares worth approximately $128,240 at the vest-date price. The exact share count depends on the per-share price; if the stock is at $200 per share, the employee receives 1,000 shares at vest, the broker sells about 358 of them to cover, and 642 remain in the account. The numbers move with the OASDI wage-base posture and whether the additional Medicare surtax is already being withheld, but the order of magnitude is consistent. The single most important editorial point in this scenario is about the W-2 and the 1099-B interaction, because this is where most employees lose money to a preventable error. The W-2 issued in January following the vest reports the full $200,000 of vest value in Box 1 as wages. That number is the basis for both the federal and California income-tax computations on the year's Form 1040 and Form 540. The broker, separately, issues a Form 1099-B for the sell-to-cover transaction — typically reporting the sale of the shares that were sold to fund withholding. Under cost-basis-reporting rules in effect since 2014, the broker is generally NOT permitted to report the wage-inclusion amount as part of the cost basis on the 1099-B for employer-equity-plan shares — the broker reports the amount the employee paid (zero, for an RSU), and the employee is required to adjust the cost basis on Form 8949 to the FMV at vest. If the employee fails to make that adjustment, the IRS computer treats the entire 1099-B proceeds as a capital gain — and taxes the same $200,000 of income twice: once on the W-2 as wages, and again as a short-term capital gain on Schedule D. This is the single most common employee equity-tax mistake. Industry surveys and brokerage education materials have repeated this point for over a decade. The fix is to enter the corrected cost basis on Form 8949 (or accept the brokerage's "supplemental statement" basis if the broker provides one) and to use Code B in column (f) to flag the adjustment if needed. For the retained shares held after the vest, the same rule applies: the cost basis is FMV at vest, and a subsequent sale produces a capital gain or loss measured against that basis. Short-term (held one year or less from the vest date) is ordinary rates; long-term (more than one year) qualifies for long-term capital-gain rates. A related complication arises if the employee relocates out of California between the vest date and the eventual sale of the retained shares. California taxes wages earned for services performed in California regardless of the employee's residency at the time the wages are paid; the RSU value at vest is wages earned for the prior service period in California and remains California-source income on Form 540 (or Form 540NR for a part-year resident) regardless of where the employee lives when the shares actually settle. The capital gain or loss on a SUBSEQUENT sale of the retained shares is a different analysis under FTB Publication 1100, "Taxation of Nonresidents and Individuals Who Change Residency" — the gain on the share appreciation after the vest date is generally sourced to the residency at the time of sale, not at the time of vest. The wage portion stays California; the share-appreciation gain follows the new state. Employees considering a move should model this carefully with a tax advisor, because the timing of the move relative to vest dates can produce non-trivial differences.

Decision tree#

1. If Did your employer accelerate any unvested RSU tranches in your severance agreement, or do you have scheduled vest dates that fall on or after the termination date?

   Then → Each vesting event is a separate inclusion event under 26 U.S.C. § 83. The fair market value on the vest date is wages, processed through payroll, subject to federal supplemental withholding at 22% (or 37% above $1M cumulative for the year), CA supplemental withholding at 10.23% under EDD DE 231PS, FICA (OASDI to the wage base + Medicare with no cap), and CA SDI at 1.3% with no taxable-wage cap since SB 951. Pull your grant agreement and the separation agreement together — the dollar amount included in each vest is the closing price (or the broker's opening trade price on the vest date) times the share count, and your W-2 for the year will show that amount in Box 1 regardless of whether you sell, hold, or have shares automatically sold to cover taxes.

   Else: If no tranches vested on or after the termination date, this scenario does not apply directly — see the related scenario on RSU forfeiture, acceleration, and clawback for the analysis of unvested tranches that are simply cancelled at separation.

2. If What is the fair market value (FMV) on the vest date, and how is it computed by your broker?

   Then → Different employers price the vest differently — most use the prior-day close, the vest-date open, or the average of the high and low on the vest date. The grant agreement and the equity plan document specify which convention applies. Capture the per-share price and the share count from the broker confirmation; multiply for the gross income amount; reconcile against the W-2 Box 1 entry when it arrives in January. A pricing mismatch is unusual but it does happen — the time to catch it is now, not in April.

   Else: If the broker statement is not yet available, request it from the equity-administration team along with the Form 3921 / 3922 / 1099-B documents that apply to your plan. The grant agreement should also specify the FMV-determination rule.

3. If How is your employer withholding on the vest — sell-to-cover, net issuance, or cash from the employee?

   Then → Sell-to-cover is the most common default at U.S. public-company plans: the broker sells enough of the just-vested shares at the vest-date market price to fund the combined withholding (federal supplemental + CA supplemental + FICA + CA SDI), and the employee retains the remaining shares. Net issuance (also called "withhold-to-cover") accomplishes the same net result without an actual market sale — the employer issues fewer shares and remits cash equivalent for withholding. Cash-from-employee is rare and would require you to fund the withholding from outside the plan. Confirm which mechanic applies before the vest date so you are not surprised by the share count that lands in your account.

   Else: If the equity administrator cannot tell you which mechanic applies, the grant agreement and the plan document are the authoritative source. Sell-to-cover is the safest default assumption at a U.S. public company.

4. If Will your cumulative supplemental wages from this employer for the calendar year — including this RSU vest plus any severance, bonus, or prior RSU settlements — exceed $1,000,000?

   Then → The federal supplemental rate on the slice above $1M jumps from 22% to a mandatory 37% per IRS Pub 15 § 7. This is the top federal individual rate, not adjustable on Form W-4, and tracked at the employer level. An accelerated RSU vest at termination is a common trigger for crossing the threshold mid-year. Coordinate with a tax advisor on Form 1040-ES estimated payments if the under-withholding produced by the rate transition will create a Section 6654 penalty exposure. California does NOT have an equivalent step-up; the 10.23% rate applies regardless of cumulative amount.

   Else: Standard 22% federal supplemental applies. The 22% rate under-withholds for any employee whose full-year marginal rate is above 22% — for a California senior IC at the 32% federal bracket, the gap is roughly 10 percentage points and produces a balance due at filing unless you have adjusted Form W-4 on remaining paychecks.

5. If After the sell-to-cover, do you intend to hold the retained shares or sell them?

   Then → The retained shares have a cost basis equal to the FMV on the vest date — the same amount your W-2 reported as wages. A subsequent sale produces a capital gain or loss measured against that cost basis. Short-term (held one year or less from the vest date) is taxed at ordinary rates; long-term (held more than one year) qualifies for long-term capital-gain treatment. The single most common employee mistake is treating the 1099-B cost basis as $0 — brokers historically reported $0 on 1099-B for employer-issued shares because they did not know the W-2 inclusion amount, and the IRS now requires Form 8949 adjustments to reconcile. If you do not adjust, you pay tax twice on the same income — once as W-2 wages and again as capital gain. See the dedicated FAQ on this.

   Else: If the sell-to-cover sold the entire vest (some plans default to "sell-all" rather than "sell-to-cover"), the analysis collapses: the W-2 reports the full vest value as wages, the 1099-B reports the sale with cost basis equal to FMV at vest, and the capital gain/loss is small (intra-day price drift only). The double-taxation trap still applies if you accept the $0 cost basis the broker may have reported — the Form 8949 adjustment is the fix.

Action steps#

• Pull the broker confirmation for every RSU vest that settles on or after your termination date. Capture the vest date, the per-share fair market value used by the plan, the gross share count, the share count sold to cover withholding, and the share count retained. The plan administrator (E*TRADE, Fidelity, Schwab, Carta, or Shareworks for most large California employers) provides this in a "trade confirmation" or "release confirmation" document. Save copies in a personal cloud folder you control, not in the employer's SSO-protected portal you may lose access to after termination.
• Verify your W-2 Box 1 wages include the RSU vest value once the W-2 arrives in January. Compute the expected inclusion as the per-share FMV at vest times the gross share count (not the post-sell-to-cover net), and reconcile against the W-2. Some employers also report the equity component in Box 14 with a code like "RSU" or "ESPP" for transparency — but Box 14 is informational only; the legally operative inclusion is Box 1. If your W-2 does not match the broker confirmation, contact stock-plan administration in the first week of February — corrections after the IRS filing deadline are materially harder.
• Track your cost basis at FMV-on-vest for every share you retain after sell-to-cover. The brokerage may report a $0 basis on the 1099-B due to cost-basis-reporting rules that prohibit the broker from including the wage-inclusion amount on the Form. You are required to adjust the cost basis on Form 8949 using your own records; many large plan administrators provide a "supplemental statement" with the corrected basis, but the legal obligation to file an accurate Form 8949 sits with the employee. Failing to adjust produces double taxation — once as W-2 wages, once as a capital gain — which is the single most common employee equity-tax mistake.
• Decide hold-versus-sell on the retained shares with the cost basis and the holding period both in view. The shares retained after sell-to-cover have a cost basis equal to FMV at vest and a holding period that starts on the vest date. A sale within one year is short-term and taxed at ordinary rates; a sale after more than one year qualifies for long-term capital-gain rates. The concentration risk of holding a large slug of post-termination employer stock is a separate analysis — diversification considerations often favor selling at or near vest, but that is a personal-finance question independent of the tax mechanics in this scenario.
• If you are considering relocating out of California before selling the retained shares, get specific guidance from a CPA on the FTB Pub 1100 residency-change analysis. The RSU value included in W-2 Box 1 is California-source wages earned for services performed in California and stays California-source on Form 540 / Form 540NR regardless of residency at payment time per FTB Pub 1031. The capital gain on the SUBSEQUENT sale of the retained shares is a separate item generally sourced to residency at the time of sale under FTB Pub 1100 — but timing and intent matter, and the FTB scrutinizes residency-change moves that closely precede large gain-realization events.
• If your cumulative supplemental wages from this employer for the year — including RSU vests, severance, bonus, and any other supplemental payments — will exceed $1,000,000, model the federal 37% step-up on the slice above the threshold before signing the separation agreement. The 37% rate is mandatory on the over-$1M portion per IRS Pub 15 § 7, not adjustable on Form W-4. The under-withholding penalty exposure under 26 U.S.C. § 6654 at that income level is meaningful, and Form 1040-ES estimated payments before the next quarterly deadline are often the right tool. California does not have an equivalent step-up — the 10.23% rate applies regardless of cumulative amount.
• File for unemployment insurance with the EDD as soon as your last day of work passes, regardless of the RSU vest size. California UI is not offset by severance pay under Cal. Unemp. Ins. Code § 1265, and RSU income is not "wages" for UI eligibility purposes either — it is settlement of a prior grant, not wages for services performed during the unemployment week. The one-week unpaid waiting period under § 1253(d) starts when the claim is filed.

FAQ#

Why does my paycheck withhold 10.23% for California on the RSU vest when severance withholds at 6.6%?

Because EDD DE 231PS specifies two different California flat rates: "For stock options and bonuses that were paid on or after November 1, 2009, the flat rate is 10.23 percent. For other types of supplemental wage payments made on or after November 1, 2009, the flat rate is 6.6 percent." RSU settlements are stock for this purpose — the vest delivers shares — and the 10.23% rate applies, the same as a year-end bonus or a stock-option exercise. Cash severance is "other supplemental wages" and uses 6.6%. A final paycheck that bundles cash severance and an RSU vest will show two separate California supplemental lines on the stub. That is correct per DE 231PS, not a payroll error. The federal side does not split the same way: IRS Pub 15 § 7 imposes a single 22% supplemental rate on both the severance and the RSU vest (up to $1M cumulative for the year, then 37% above).

Is the 10.23% California withholding rate the actual tax I owe on the RSU vest?

No — it is a paycheck-mechanics default. Your actual California liability is computed on Form 540 using graduated brackets and reconciled at filing. For a senior IC whose taxable income falls in the upper California brackets near the supplemental rate, the 10.23% flat is approximately right — slightly over-withholding for income that sits below it on Form 540 and slightly under for income that sits in higher graduated bands. The federal side is where the gap usually opens up: 22% supplemental against an upper-bracket Form 1040 marginal rate (top brackets run through the 30s) under-withholds by about 10 percentage points or more, producing a balance due at filing. Plan on that gap unless you have adjusted Form W-4 on remaining paychecks (RSU settlements themselves are typically paid at the flat supplemental rate; you cannot override the 22% default on the equity check itself in most payroll systems).

My 1099-B shows a cost basis of $0 on the shares the broker sold to cover withholding. Is that right?

No, and this is the single most common employee equity-tax mistake. The cost basis of every share that vested is the fair market value on the vest date — the same amount that your W-2 reported in Box 1 as wages. Under cost-basis-reporting rules in effect since 2014, the broker is generally NOT permitted to report the wage-inclusion amount as part of the cost basis on Form 1099-B for employer-equity-plan shares; the broker reports the amount you paid for the shares, which for a standard RSU is zero. You are required to adjust the cost basis on Form 8949 to FMV-at-vest using your own records. Many plan administrators provide a "supplemental statement" with the corrected basis to make the adjustment easier, but the legal responsibility to file an accurate Form 8949 sits with you. Failing to adjust means you pay tax twice on the same income — once as W-2 wages, and again as a short-term capital gain on Schedule D against a $0 cost basis. Use Form 8949 column (g) to enter the adjustment and column (f) to flag it (Code B for a basis reported incorrectly by the broker).

What does "sell-to-cover" actually mean, and can I opt out of it?

Sell-to-cover is the default broker mechanic for funding withholding on an RSU settlement at most U.S. public-company plans. On the vest date, the broker computes the total withholding due (federal supplemental + CA supplemental + FICA + CA SDI), divides by the vest-date per-share price, and sells exactly enough shares at the open market to remit the withholding to the employer's payroll system. The employee retains the remaining shares. Some plans offer alternatives: "net issuance" (also called "withhold-to-cover") accomplishes the same net result without an actual market sale — the employer issues fewer shares and remits cash equivalent; "sell-all" sells the entire vest and delivers cash; "cash-from-employee" requires you to fund the withholding from outside the plan. Whether you can change the default depends on the plan document and your employer's administrator settings — request the alternatives in writing from stock-plan administration before the vest date, because changes after the fact are usually not allowed.

My RSU vest will push me over $1 million in total supplemental wages for the year. What happens?

The federal supplemental rate on the portion above $1,000,000 cumulative for the calendar year jumps from 22% to a mandatory 37% per IRS Pub 15 § 7. This is the top federal individual rate and is not optional or adjustable on Form W-4. The threshold is tracked at the employer level: if you have supplemental wages from two unrelated employers totaling more than $1M but neither employer individually crosses, the gap is reconciled on Form 1040 at filing — usually with a substantial balance due. An accelerated RSU vest at termination is a common mid-year trigger for crossing the threshold, especially when stacked with severance and a final-year bonus. California does NOT have an equivalent step-up; the 10.23% rate applies regardless of cumulative amount. Coordinate with a tax advisor on Form 1040-ES estimated-tax payments — the under-withholding penalty under 26 U.S.C. § 6654 is meaningful at this income level.

If I move out of California after my RSUs vest but before I sell the retained shares, where do I pay tax?

The W-2 wage portion stays California-source regardless of where you live when the shares actually settle in your account. FTB Publication 1031 explains the underlying rule: California taxes wages earned for services performed in California regardless of the employee's residency at payment time. An RSU is compensation for the service period leading up to vest, so the vest-date FMV included in W-2 Box 1 is California-source wages on your Form 540 (or Form 540NR if you are a part-year resident). The capital gain or loss on the SUBSEQUENT sale of the retained shares is a different analysis under FTB Publication 1100 — share-appreciation gain after the vest date is generally sourced to your state of residence at the time of sale, not at the time of vest. Practical implication: a move that immediately precedes the vest does not change the California tax on the vest, but a move that occurs after the vest and before the sale generally does shift the post-vest gain to the new state. Model the specific timing carefully with a CPA, because the FTB scrutinizes residency-change moves that closely precede large gain-realization events.

Do FICA and CA SDI apply to RSU settlements at termination?

Yes to both. OASDI (6.2% employee) applies up to the 2026 Social Security wage base of $184,500 published by SSA. A senior IC at $220,000 base salary will typically have crossed the wage base on a regular paycheck before a mid-year termination, in which case OASDI on the RSU vest is zero. Medicare (1.45%) applies to the full vest value with no wage cap. The additional 0.9% Medicare surtax under 26 U.S.C. § 3101(b)(2) kicks in once cumulative Medicare wages cross $200,000 single or $250,000 MFJ; the employer begins withholding the surtax once the employee's YTD Medicare wages with that employer cross $200,000, which very commonly applies on a senior-IC accelerated vest. CA SDI is the California-specific always-on layer: SB 951 eliminated the SDI taxable-wage cap effective January 1, 2024, and per the EDD Rates page: "The SDI withholding rate for 2026 is 1.3 percent." A $200,000 RSU vest produces $2,600 of SDI regardless of YTD wages because the cap is gone.

My employer accelerated my RSU vest in the severance agreement. Does that change the tax treatment?

No — acceleration changes the timing of the income event, not the character of the income. The accelerated vest is treated the same as a scheduled vest for tax purposes: ordinary income at FMV on the (accelerated) vest date under 26 U.S.C. § 83, federal supplemental withholding at 22% (or 37% above $1M cumulative) per IRS Pub 15 § 7, California supplemental withholding at 10.23% per EDD DE 231PS, FICA, and CA SDI. The cost basis on the retained shares is FMV at the accelerated vest date. One nuance: if the accelerated grant is performance-vesting or otherwise treats as nonqualified deferred compensation, the acceleration provision in the separation agreement should be drafted carefully under IRC § 409A to qualify for the involuntary-separation-pay exception or another exception — an improperly drafted acceleration of NQDC can trigger a 20% excise tax and immediate income inclusion on the full deferred amount. Standard time-vesting RSUs at most public companies are not subject to § 409A because the settlement is within 2.5 months of the year of vest, but performance units and certain executive RSU grants warrant a closer look.

Sources#