Stock Options and RSUs in Multi-State Work: A Complete Tax Guide

Equity compensation is the single most complex multi-state tax issue faced by employees of technology companies, financial institutions, and other equity-heavy employers. A single RSU vest can produce six figures of income sourced to multiple states under a workday fraction allocation, and the rules differ by equity type (RSU, NSO, ISO, ESPP) and by state (California, New York, Pennsylvania, and Massachusetts each have unique sourcing rules). The consequences of getting the allocation wrong include underpayment penalties, double taxation, and audit exposure that can stretch back six years or more.

This guide covers the federal taxation of each equity type, the multi-state allocation method, three worked examples spanning the most common scenarios, and the state-specific rules that complicate the picture. Every rule cited is current as of 2025, with references to the controlling IRC sections, IRS publications, and state statutes.

The multi-state equity compensation problem

The multi-state equity problem arises because equity compensation is taxed in stages, and each stage can be sourced to a different state. RSUs produce ordinary income at vesting, then capital gains or losses when the shares are sold. NSOs produce ordinary income at exercise (the spread between exercise price and fair market value), then capital gains or losses when sold. ISOs produce no regular tax at exercise but trigger the alternative minimum tax, then capital gains when sold. ESPPs produce ordinary income at sale equal to the discount, plus capital gains on the appreciation above the discount.

For each stage, the state sourcing question is: where was the employee resident, and where was the work performed, on the date the income was recognized? For ordinary income at vesting or exercise, most states use the workday fraction method — the ratio of workdays performed in each state during the vesting period to total workdays in the vesting period. For capital gains at sale, the income is sourced to the state of residence on the sale date, regardless of where the work was performed. The combination produces a complex multi-state allocation that few employees and many tax preparers get right on the first try.

The dollar stakes are high. A California resident with a $300,000 RSU vest faces approximately $40,000 in California tax at 13.3% on the vesting income. If the same employee had moved to Texas one month before vesting, the post-move workdays are allocated to Texas (no tax), and the California tax is reduced by approximately 8% (one month out of twelve). The savings from correct timing and allocation can run into tens of thousands of dollars per vest event.

Types of equity: NSO, ISO, RSU, ESPP

Non-qualified stock options (NSOs) are options to purchase employer stock at a fixed exercise price. NSOs are taxed at exercise under IRC §83: the spread between the exercise price and the fair market value on the exercise date is ordinary wage income, subject to federal income tax, FICA under IRC §3101, and federal unemployment tax. The employer reports this amount in Box 1, 3, and 5 of Form W-2 and withholds federal and state income tax at the supplemental rate. When the shares are subsequently sold, the appreciation above the fair market value at exercise is capital gain (short-term if held one year or less, long-term if held more than one year).

Incentive stock options (ISOs) are options that meet the requirements of IRC §422. ISOs produce no regular federal tax at exercise, but the bargain element (the spread between exercise price and fair market value at exercise) is an AMT preference item under IRC §56(b)(3). If the shares are held for at least two years from the grant date and one year from the exercise date, the entire gain (bargain element plus subsequent appreciation) is long-term capital gain. If the holding periods are not met, a "disqualifying disposition" recharacterizes the bargain element as ordinary wage income.

Restricted stock units (RSUs) are promises to deliver shares of employer stock at a future date, subject to vesting conditions. RSUs are taxed at vesting under IRC §83(a): the fair market value of the shares on the vesting date is ordinary wage income, reported in Box 1 of Form W-2 and subject to federal and state withholding. There is no IRC §83(b) election available for RSUs because there is no substantial risk of forfeiture on the share value once the units vest. The shares received at vesting have a basis equal to the ordinary income recognized.

Employee stock purchase plans (ESPPs) under IRC §423 allow employees to purchase employer stock at a discount (typically 15%) through after-tax payroll contributions. The tax treatment depends on whether the holding periods are met. For a qualifying disposition (held more than two years from the offering date and more than one year from the purchase date), the discount is ordinary income and the appreciation above the purchase price is long-term capital gain. For a disqualifying disposition, the discount is ordinary wage income and the remaining gain is short- or long-term capital gain depending on holding period from the purchase date.

RSU taxation: ordinary income at vesting; multi-state allocation by work days

The ordinary income at RSU vesting is sourced to each state using the workday fraction method. The numerator is the number of workdays performed in the state during the vesting period. The denominator is the total workdays in the vesting period. The vesting period for an annual vest that occurs on January 15, 2026, runs from January 16, 2025 (the prior vesting date) through January 14, 2026 (the day before the current vesting date). Workdays performed in any state during that 365-day period are allocated to that state.

California conforms to the workday fraction method under FTB Legal Ruling 2003-3 and Cal. R&TC §17014. New York conforms under Tax Law §631(b) and TSB-M-06(5)I. Pennsylvania conforms under 72 P.S. §7301. The mechanics are similar across states, but the documentation requirements differ. California requires a detailed workday allocation worksheet (Form 3500 for non-residents) showing day-by-day work locations. New York requires Form IT-203B Schedule A. Pennsylvania accepts a summary allocation but reserves audit rights for three years.

The employer's role is to withhold state income tax at vesting based on the employee's state of residence on the vesting date, not based on the workday allocation. This means a Texas resident who worked 50% of the vesting period in California will have no California withholding at vesting but will owe California non-resident tax on the California-allocated portion. The employee must make California non-resident estimated tax payments to cover the liability, or face underpayment penalties at 8% annualized.

NSO taxation: ordinary income at exercise; spread

NSO exercise produces ordinary income equal to the spread between the exercise price and the fair market value on the exercise date. The spread is wage income under IRC §83(a), reported in Box 1, 3, and 5 of Form W-2. Federal income tax is withheld at the supplemental rate of 22% (or 37% for amounts over $1 million under IRC §3402(g)(6)(A)). FICA is withheld at the combined employer-employee rate of 7.65% (6.2% Social Security up to the wage base of $176,100 in 2025, plus 1.45% Medicare), with the Additional Medicare Tax of 0.9% on wages over $200,000 single or $250,000 married filing jointly under IRC §3101(b)(2).

The multi-state allocation for NSO ordinary income uses the workday fraction method, but the vesting period is more complex. The IRS position (Rev. Rul. 79-305) and California FTB Legal Ruling 2003-3 take the position that the vesting period for an NSO is the entire period from grant to exercise, not just the period from the last vesting date to exercise. This means that an employee who worked in California for four years before an option grant, then moved to Texas and exercised five years later, must allocate the spread at exercise to California for the workdays performed in California during the entire grant-to-exercise period.

The alternative position, advanced by some practitioners, is that the vesting period is only the period during which the option was unvested. Under this view, an option that vested in full two years before exercise would have a vesting period ending two years before exercise, and workdays after vesting would not be allocated. California FTB audit practice generally rejects this position and applies the grant-to-exercise allocation.

ISO taxation: no regular tax at exercise; AMT

ISO exercise produces no regular federal tax in the year of exercise, but the bargain element is an AMT preference item under IRC §56(b)(3). The AMT calculation under IRC §55 adds the bargain element to regular taxable income, applies the 26% or 28% AMT rate, and produces AMT liability to the extent AMT exceeds regular tax. The AMT is partially recoverable in future years as a minimum tax credit under IRC §53.

The multi-state AMT treatment varies. California conforms to the federal AMT under R&TC §17062, with a California AMT rate of 7%. New York conforms under Tax Law §629, applying the federal AMT calculation with state modifications. Massachusetts does not conform to AMT, so the ISO bargain element produces no Massachusetts AMT. Pennsylvania does not allow the federal AMT, but Pennsylvania also does not tax ISO exercises at all under 72 P.S. §7303(a)(7) (because there is no realization event for Pennsylvania until sale).

The state sourcing for the AMT preference follows the wage sourcing for the underlying ISO exercise. If the employee was a California non-resident who performed 30% of workdays in California during the grant-to-exercise period, 30% of the bargain element is California-source AMT preference. The California AMT calculation produces a California AMT liability on that portion. This can create a significant California tax liability even though no California regular tax is due.

ESPP taxation: discount as ordinary income

ESPP taxation depends on the holding period. For a qualifying disposition (held more than two years from offering date and more than one year from purchase date), the discount is ordinary income reported on Form W-2 Box 1 (in most cases) or as an adjustment on Form 1040 Schedule 1 (if the employer did not include it in W-2). The appreciation above the purchase price is long-term capital gain. For a disqualifying disposition, the discount is ordinary wage income reported in W-2 Box 1, and the remaining gain is capital gain (short or long depending on holding period from purchase).

The multi-state sourcing for ESPP income follows the workday fraction method, applied to the offering period (typically 6 to 24 months for a Section 423 plan). The offering period is the period from the offering date to the purchase date. Workdays performed in a state during the offering period are allocated to that state for the discount portion of the income. The capital gain on sale is sourced to the state of residence on the sale date.

California does not conform to the federal ESPP rules in all respects. Under R&TC §17071, California follows the federal treatment for qualifying dispositions but treats the entire gain on a disqualifying disposition as ordinary income to the extent of the discount, with no capital gain until the discount is recaptured. Pennsylvania follows the federal treatment under 72 P.S. §7303(a)(6).

Multi-state allocation for equity: the workday fraction method

The workday fraction method is the universal approach to allocating equity income across states. The calculation is: state-source equity income = total equity income × (workdays in state during vesting period / total workdays during vesting period). The vesting period is defined by state: California uses grant-to-vest for RSUs and grant-to-exercise for options; New York uses the same; Pennsylvania uses a similar approach.

Workdays include all days the employee was performing services for the employer, including telework days, business travel days, and paid holiday days. Workdays do not include weekends, vacation days, sick leave, or other non-working days. The total workdays in a typical year is approximately 250 (52 weeks × 5 days, less holidays). The denominator is the total workdays across all states, not the total days in the period.

Documentation is critical. The employee should maintain a contemporaneous day-count calendar showing physical work location for each workday. The calendar should be backed up by airline boarding passes, hotel receipts, credit card transaction locations, and cell phone tower data. Employer-issued workday allocation statements (often produced for SEC reporting purposes) are useful corroboration but are not conclusive in a state audit.

Worked example 1: CA resident with RSUs vesting while working remotely

A California resident employee of a public tech company has a $200,000 RSU vest on March 15, 2025. The vesting period runs from March 16, 2024 (prior vest) through March 14, 2025. Total workdays in the vesting period: 245. Of those, 200 days were worked in California (the employee's home office in San Francisco), 30 days were worked in New York (client visits to the company's New York office), and 15 days were worked in Texas (a one-week client engagement plus a vacation week that included some work).

The allocation: California source = $200,000 × (200/245) = $163,265. New York source = $200,000 × (30/245) = $24,490. Texas source = $200,000 × (15/245) = $12,245. California taxes the full $200,000 because the employee is a California resident (California taxes residents on worldwide income). California allows a credit for taxes paid to other states under R&TC §18001, so the $24,490 New York source produces New York non-resident tax of approximately $2,400 (at 9.85% marginal rate) and a corresponding California credit of $2,400. The Texas source produces no Texas tax (no income tax) and no California credit. The net California tax on the vest is approximately $26,000 ($200,000 × 13.3% minus $2,400 credit), and the net New York tax is approximately $2,400.

The employer withholds California tax at 10.23% supplemental rate on the full $200,000 at vesting, or $20,460. The employee owes an additional $5,540 to California at filing plus $2,400 to New York (which had no withholding because the employee never had a New York address). The employee should make California estimated tax payments to cover the $5,540 shortfall and New York non-resident estimated tax payments on Form IT-2105 to cover the $2,400.

Worked example 2: NY resident with ISOs and AMT

A New York resident exercises 10,000 ISOs on June 15, 2025, when the fair market value is $50 per share and the exercise price is $10 per share. The bargain element is ($50 - $10) × 10,000 = $400,000. No regular federal or state tax is due at exercise. The AMT preference is $400,000.

Federal AMT calculation: The employee has regular taxable income of $250,000 (wages minus deductions). AMT income = $250,000 + $400,000 = $650,000. Less AMT exemption of $92,700 (2025 single exemption, phased out above $626,350 AMTI) = $557,300. AMT at 26% on first $239,100 and 28% above = $62,166 + $89,052 = $151,218. Regular tax is approximately $53,000, so AMT liability is $151,218 - $53,000 = $98,218.

New York AMT calculation under Tax Law §629: New York conforms to federal AMT with state modifications. The federal AMT preference of $400,000 flows through to New York AMT income. New York AMT rate is 28% of the federal tentative minimum tax (or the federal AMT rate applied to New York-source income, depending on residency). For a full-year New York resident, the New York AMT is approximately $26,000. The employee must make New York estimated tax payments to cover this AMT liability, because no withholding occurs at ISO exercise. New York underpayment penalty runs 7.5% annualized.

The minimum tax credit under IRC §53 is generated: $98,218 of federal AMT paid becomes a minimum tax credit carryforward, recoverable in future years when regular tax exceeds AMT. New York has a similar minimum tax credit under Tax Law §629(e). The credit can recover the AMT over 5-10 years depending on future income.

Worked example 3: Employee who moved mid-year with unvested RSUs

An employee of a Massachusetts-based company moves from Massachusetts to New Hampshire on July 1, 2025. The employee has a $150,000 RSU vest on December 15, 2025. The vesting period runs from December 16, 2024 through December 14, 2025, totaling 245 workdays. The employee worked 122 workdays in Massachusetts (January 1 through June 30, less holidays and vacation) and 123 workdays in New Hampshire (July 1 through December 14).

The allocation: Massachusetts source = $150,000 × (122/245) = $74,694. New Hampshire source = $150,000 × (123/245) = $75,306. Massachusetts taxes the $74,694 as non-resident income at 5%. New Hampshire has no income tax on wages (the New Hampshire interest and dividends tax was fully repealed effective January 1, 2021). Massachusetts tax = $74,694 × 5% = $3,735.

The employer withholds Massachusetts tax at 5% on the full $150,000 at vesting (because the employee was a Massachusetts resident at the start of the vesting period and the employer has not updated the records). The employee files a Massachusetts part-year resident return showing the pre-move Massachusetts-source income including $74,694 of the RSU vest, and claims a refund of the over-withheld Massachusetts tax on the New Hampshire-allocated portion (approximately $3,765). The employee has no New Hampshire tax liability.

The remaining $75,306 of the vest (the New Hampshire-allocated portion) is federal taxable income and Massachusetts part-year-resident non-taxable income, but the employee must be careful to report the full $150,000 as federal wages and only $74,694 as Massachusetts wages on Schedule HC (Health Care) and Form 1-NR/PY. The basis in the 1,500 shares received (assuming $100 share price) is $150,000 for federal purposes, and the holding period begins on December 15, 2025.

State-specific rules: CA source rules; NY convenience rule on equity; PA source rules

California source rules for equity compensation are detailed in FTB Legal Ruling 2003-3 and FTB Schedule CA instructions. California uses the workday fraction method for RSUs and NSOs, allocating ordinary income based on workdays performed in California during the vesting period. For ISOs, California does not tax the exercise event for regular tax purposes (conforming to federal) but does generate California AMT under R&TC §17062, with the AMT preference sourced to California based on the workday fraction during the grant-to-exercise period. California does not recognize the Section 83(b) election for restricted stock in some circumstances.

New York applies the convenience rule to equity compensation under 20 NYCRR 132.16. If a non-resident employee works remotely from outside New York for the employee's own convenience, the wage income (including equity compensation ordinary income) is sourced to New York regardless of the physical work location. This means a New Jersey resident who telecommutes to a New York employer has the full RSU vest amount sourced to New York, even if zero workdays were performed in New York. The convenience rule does not apply to capital gains on the subsequent sale of the shares, which are sourced to the state of residence on the sale date.

Pennsylvania source rules for equity are unusual. Under 72 P.S. §7303(a), Pennsylvania does not tax the exercise of ISOs at all (no realization event until sale). Pennsylvania taxes NSO exercises and RSU vests as wage income, with the workday fraction allocation. Pennsylvania has a 3.07% flat tax rate, the lowest among states with broad-based income taxes. Pennsylvania withholding on non-resident equity income is 3.07%, generally adequate to cover the liability.

Common mistakes: forgetting state allocation; missing estimated payments

The most common multi-state equity mistake is failing to allocate the vest or exercise income across multiple states. Employees with a single W-2 state often assume the equity income is also single-state, but the workday fraction can produce significant allocations to states where the employee occasionally worked. The fix is to maintain a contemporaneous workday calendar and to prepare the state-by-state allocation worksheet before the tax return is filed.

The second most common mistake is missing state estimated tax payments. Employers withhold state tax only for the employee's state of residence on the vesting date. If the workday allocation produces income sourced to a non-residence state, the employee must make non-resident estimated tax payments to that state to cover the liability. The underpayment penalty runs 6-10% annualized depending on the state. The safe harbor for most states is 90% of current-year tax or 100% of prior-year tax (110% if AGI exceeds $150,000).

The third common mistake is mishandling the basis reporting on the subsequent sale of the shares. The basis for federal purposes is the fair market value at vesting (for RSUs) or the exercise price plus the spread recognized as ordinary income (for NSOs). The basis for state purposes may differ if the state did not tax the ordinary income at vest (e.g., a Texas resident who moved from California has a California-source portion of the vesting income but the entire basis for state capital gain purposes is the vesting fair market value). Failing to adjust the basis on the state return can produce double taxation.

Year-end planning for equity

Year-end equity planning has three components. First, evaluate the timing of discretionary exercises (NSOs and ISOs) — exercising in December 2025 versus January 2026 can shift the income into a different tax year. Second, evaluate the timing of sales — selling appreciated shares in 2025 locks in the capital gain at 2025 rates, while selling in 2026 may produce different rates if the TCJA rate sunset takes effect. Third, evaluate the timing of charitable donations of appreciated shares — donating shares held more than one year produces a deduction for the full fair market value under IRC §170(e)(1) and avoids capital gains tax on the appreciation.

For employees with a planned residency change, the timing of equity events relative to the move is critical. An RSU vest in December 2025 while resident in California produces California tax on the workday-allocated portion. The same vest in January 2026 after a move to Texas still produces California tax on the workdays performed in California during the vesting period, but the post-move workdays are allocated to Texas (no tax). The savings is roughly proportional to the post-move workdays.

Audit defense

State DORs are increasingly auditing equity income allocations because the dollar amounts are large and the workday fraction is often undocumented. California FTB and New York DTF both have dedicated equity compensation audit teams. The audit typically opens with a request for the workday allocation worksheet and supporting documentation.

The defense is a contemporaneous workday calendar backed by independent records. The calendar should show, for each workday in the vesting period, the physical work location. The calendar should be backed by airline boarding passes, hotel receipts, credit card transaction locations, and cell phone tower data (which can be obtained from the carrier). Employer-issued workday allocation statements are useful corroboration but are not conclusive because they are typically prepared by the employee and submitted to the employer.

If the workday calendar is missing or incomplete, the Cohan rule (39 F.2d 540, 2d Cir. 1930) allows reasonable estimates where exact records are unavailable, but the estimate must be based on credible evidence. A reconstructed calendar from credit card statements and travel records is more credible than a calendar reconstructed from memory. If the audit produces a deficiency, the taxpayer can request an abatement of penalties for reasonable cause, but interest accrues regardless.

What to do next

Open the WithholdRight calculator to project the federal and state tax impact of any equity events in 2025. Identify the workday allocation for each vesting period and confirm that estimated tax payments have been made to each state with a source claim. If you are planning a residency move before an equity event, document the move before the event and update your employer's records.

Gather the equity grant agreements, vesting statements, exercise statements, and the workday calendar for each vesting period in the past three years. If the workday allocation was not done correctly on prior-year returns, consult a tax professional about amending under the IRC §6511 three-year statute of limitations.

Every equity event with a multi-state dimension should be reviewed by a licensed tax professional who understands both the federal equity rules and the state sourcing rules. The WithholdRight calculator handles the projection; the planner handles the strategy and the documentation. Use both.