Multi-State Tax Returns: California Sourcing, Remote Work, and Equity Across State Lines

You are sitting at your kitchen table in San Jose, logged into a Zoom call with your New York-based employer. You are earning a California wage, but your W-2 says New York. You moved to California from Washington state two years ago, and your RSUs are vesting now from grants made while you lived in Seattle. You have been in California for 18 months and nobody has explained how your tax situation actually works.

The honest answer: you may owe tax in two states on the same income. And the credit that is supposed to prevent that double taxation only partially works, in ways that depend on each state's specific rules. Getting multi-state returns wrong is expensive. The IRS matching programs catch income sourced to one state that was reported in another. California is aggressive about auditing nonresident sourcing for high-income individuals. The notices arrive 12 to 36 months after the original return, with interest running the whole time.

Silicon Valley Tax prepares multi-state returns for Bay Area residents, remote workers, and tech employees with equity compensation vested across multiple states. Our office is at 2051 Junction Ave, San Jose. Call (408) 383-9870 or book a free consultation to discuss your specific situation.

California Income Tax Basics: Residency and Sourcing

California taxes income on two bases. First, if you are a California resident, California taxes your worldwide income for the period you are a resident. Second, even if you are a nonresident, California taxes income sourced to California. These two concepts operate independently and can apply to the same dollar of income.

What Makes You a California Resident?

Under California Revenue and Taxation Code Section 17014, a resident is any individual who is in California other than for a temporary or transitory purpose, and any individual domiciled in California who is outside California for a temporary or transitory purpose. Domicile means your permanent home, the place you intend to return to. Residence is a fact question based on where you actually live.

California uses a "closest connection" test for disputed cases. Factors include: location of your home, where your spouse and children live, where your vehicles are registered, where your bank accounts are held, where you are registered to vote, where you hold professional licenses, where your employer is located, and where you spend the most time. High-income individuals who try to claim Nevada or Texas residency while spending most of the year in California find that the Franchise Tax Board audits these claims aggressively.

Part-Year Residency

If you move to California or leave California during the year, you are a part-year resident. You file California Form 540NR (Nonresident or Part-Year Resident Return). As a part-year resident, you owe California tax on:

• All income earned while you were a California resident, regardless of the source or location of the income
• California-sourced income earned after you left California, even as a nonresident

The second point catches many people off guard. If you move to Texas in July and receive a bonus in October for work performed while you were in California, that bonus is California-sourced. If your RSUs vest in November based on a grant-to-vest period that includes California days, the California-apportioned portion of the vest is California-sourced income. You will owe California tax on those amounts even though you are now a Texas resident.

California Sourcing Rules That Matter for Bay Area Tech Workers

Wage Income: Where Services Are Performed

Wages are sourced to where you perform the services. If you are a California resident working from a home office in San Jose, your wages are California-sourced income, regardless of where your employer is incorporated or headquartered. This is the baseline rule.

The complication arises when you travel to perform services in other states. Business trips to New York, Texas, or any other state create a sourcing issue: the days you work physically in that state may be sourced there, not to California. Each state has its own rules about whether short-term business visitors are taxable, and most states have de minimis thresholds before they claim nonresidents.

RSU Sourcing: The Grant-to-Vest Apportionment

RSU income is sourced to the states where you performed services during the period from grant date to vest date. California Franchise Tax Board Publication 1005 describes the apportionment method: divide California workdays during the grant-to-vest period by total workdays, then multiply that fraction by the total RSU vest income.

Example: You were granted 1,000 RSUs on January 1, 2022, while living in Austin, Texas. The RSUs vest on January 1, 2025 (three-year cliff vest). You moved to San Jose in January 2024. At vest, the stock is worth $80,000.

• Total grant-to-vest period: 1,096 days
• California workdays (January 2024 through December 2024): approximately 250 days
• California fraction: 250 / 1,096 = 22.8%
• California-sourced RSU income: $80,000 x 22.8% = $18,240
• This $18,240 is California-sourced income even if you moved back to Texas before the vest date

Many tech employees moving to California mid-vesting period do not realize they are creating California tax exposure on grants that predate their California residency. Conversely, employees leaving California carry a California-source tail on unvested grants that continues until vest date.

ISO and NSO Sourcing

Incentive stock options present a more complex sourcing picture. For AMT purposes, the ISO spread at exercise is sourced to where services were performed during the grant-to-exercise period (similar to the RSU apportionment). For California regular income tax, California applies the same grant-to-exercise apportionment to the ISO spread on the California nonconforming income recognition (since California taxes ISOs at exercise as ordinary income).

For nonqualified stock options (NSOs), the spread at exercise is ordinary income sourced to where services were performed during the grant-to-exercise period. If you were in California for any portion of that period, California will claim its proportionate share.

When you eventually sell the shares, the gain on sale (the appreciation from the FMV at exercise to the sale price) is investment income sourced to your state of residence at the time of sale, not to where you worked during the option period.

The Convenience of the Employer Doctrine

The most aggressive multi-state tax doctrine that affects Bay Area remote workers comes from New York. Under New York's convenience of the employer rule, if you work from home in California for a New York employer, New York asserts that your wages are New York-sourced income unless you work from home because of a necessity required by your employer, not merely for your own convenience.

New York's standard for employer necessity is strict. The fact that your employer allows you to work remotely, or that your position is listed as remote, is not enough. You generally need to show that your employer has a legitimate business reason requiring you to work from a location outside New York, such as needing to serve a California client base or having a California-based operation that requires your physical presence.

States that apply convenience of the employer rules (with variations):

• New York: The strictest version. Work from home in California = New York wages unless employer necessity is established. New York aggressively enforces this against high earners who have tried to establish residency elsewhere.
• Massachusetts: Applied the convenience rule broadly during the COVID-19 pandemic for employees who moved out of state and never fully returned. The specifics depend on the tax year.
• Delaware: Similar convenience-based sourcing that can create double taxation for Bay Area residents working for Delaware-based companies.
• Nebraska and Pennsylvania: Apply their own versions of the convenience doctrine.

California provides a credit for taxes paid to other states on Schedule S. But the credit is limited to the California tax computed on that income, and the computation is proportionate. If the other state has a higher rate than California's effective rate on that income, the credit does not fully eliminate the double taxation.

Credit for Taxes Paid to Other States: Schedule S

California Schedule S calculates the credit available for taxes paid to another state on income also taxed by California. The credit is designed to prevent double taxation, but it does not always achieve that result because the credit is capped.

The credit formula:

1. Calculate California tax on the net income taxed by the other state
2. Calculate the tax actually paid to the other state on that same income
3. The credit is the lesser of (1) and (2)

If you paid $8,000 to New York and California's proportionate tax on that same income is $9,300, you get the full $8,000 credit and pay $1,300 net to California. If California's proportionate tax is only $6,500, you get a $6,500 credit and effectively have $1,500 of double taxation on the New York side.

Important limits on Schedule S:

• The credit applies only to net income taxes paid to another state or country. Tax credits, withholding, and estimated payments in the other state reduce the net tax paid used in the calculation.
• You must file the other state's return before claiming the credit. California FTB requires the other state return to be available for audit.
• The credit is computed separately for each state. If you have income taxed by three states, you compute three separate Schedule S calculations.
• The credit does not apply to city or local income taxes (like New York City tax), only to state-level income taxes.

Allocation and Apportionment for Business Income

Bay Area residents who own businesses operating in multiple states face a different set of rules from wage earners. Business income is generally apportioned among states based on formulas that look at the ratio of a business's sales, payroll, and property in each state to its total sales, payroll, and property nationwide. California uses a single-sales factor apportionment formula for most business types under California Revenue and Taxation Code Section 25128.7.

For Bay Area entrepreneurs, consultants, and small business owners:

• Single-member LLCs and sole proprietors report business income on Schedule C. California taxes all income if you are a California resident. If you have business activities in other states that create nexus in those states, you may owe additional state filings.
• S corporations and partnerships file entity-level returns in each state where they have nexus. Income flows to you via K-1, and your individual return then handles the multi-state allocation. California's single-sales factor formula typically results in a larger California apportionment fraction for service businesses that sell to California customers.
• California economic nexus. California has enacted economic nexus rules that pull businesses with California-based sales into California's tax net even without physical presence in the state. This matters for Bay Area business owners with customers in other states who need to consider the reverse: their out-of-state customers' states may claim nexus over them.

Bay Area-Specific Multi-State Scenarios We Handle Most Often

Remote Workers for Out-of-State Employers

The classic situation since 2020: Bay Area tech worker hired by a New York, Seattle, Austin, or Chicago company under a remote arrangement. They live and work in San Jose or Oakland but their W-2 is issued in the employer's home state. For employers in no-income-tax states (Washington, Texas, Florida), there is no double taxation issue for wages. For New York and Massachusetts employers, the convenience doctrine creates real risk.

We prepare the California resident return, file the other state's nonresident return where required, and compute Schedule S to claim the credit. We also advise on whether it is worth making the employer necessity argument to New York, which requires documentation from the employer about the business rationale for the remote arrangement.

Mid-Year California Moves: In and Out

Tech workers move into California for a new job at a Bay Area company and leave California when they take a remote role or move for family reasons. The move-in scenario creates immediate issues with RSU vesting on grants that began before they arrived. The move-out scenario creates ongoing California-source exposure on unvested equity.

We build a multi-year projection of California-sourced income for clients who are planning to leave California, so they understand the tail of state tax obligations that follows them even after establishing residency elsewhere.

Tech Employees With Stock That Vested Across Multiple States

An engineer joins a Bay Area company in 2021 on a four-year RSU grant. In 2022 they take an internal transfer to the Austin office. In 2023 they return to San Jose. By 2025, each annual vest tranche has a different California apportionment fraction based on where they worked each year during the grant period. All four vests in the same year can have four different California percentages.

We track the grant-to-vest apportionment for each RSU tranche and reconcile it against the brokerage's 1099-B and supplemental statement. Brokerage houses routinely get the state apportionment wrong on the supplemental statements, either over-reporting California income or under-reporting it. Accepting the brokerage's number without checking it is one of the most common errors on tech-employee returns.

Non-Resident Rental and Real Estate Income

Bay Area residents who own rental property in other states must file nonresident returns in those states to report rental income. Conversely, nonresidents who own California rental property owe California tax on that income even after leaving the state. If you sold your California home when you moved and are wondering whether the gain is California-sourced after you leave: yes, gain from the sale of California real estate is always California-sourced, regardless of where you live at the time of sale.

How We Prepare Multi-State Returns

Our multi-state return process includes:

1. Residency analysis. Confirm your domicile and residency status for each state where you have potential obligations. For part-year returns, identify the exact move dates and document them.
2. Income sourcing map. For each income item, determine the state-by-state sourcing allocation. Wages by workday diary (if needed), RSUs by grant-to-vest apportionment, options by grant-to-exercise apportionment, investment income by residence state.
3. Nexus review. Identify all states where you have a filing obligation. This includes states where you physically worked, states with equity sourcing claims, and states where your business has nexus.
4. Return preparation. Prepare California resident or part-year return first. Then prepare nonresident returns for other states in the correct order, because the credit on Schedule S depends on the other state's tax figures.
5. Credit computation. Calculate Schedule S credits for each state. Verify that the credits are correctly limited to the lesser of California's proportionate tax or the other state's tax actually paid.
6. Withholding reconciliation. Many employees have withholding for the wrong state or insufficient California withholding on equity income. We reconcile withholding and set up estimated tax payments where needed.

Documents You Need for a Multi-State Return

• W-2s from all employers, noting the state box amounts (Box 15 shows the state and Box 16 shows state wages)
• Brokerage 1099-B and supplemental statements with RSU and option vest details by date
• RSU grant agreements and equity platform statements (Carta, Shareworks, Fidelity Equity) showing grant date, vest dates, vest prices, and state apportionment if provided
• For part-year moves: documentation of move dates (lease agreements, utility transfer dates, driver's license change date)
• Prior-year state returns, especially if you have carryforward losses or credits in any state
• For the convenience doctrine argument: any employer documentation about the business necessity of your remote arrangement
• K-1s from partnerships or S corporations showing state-level income amounts
• Travel logs if you work in multiple states regularly (some taxpayers need to track workday counts)

Common Errors on Multi-State Returns

We see these errors most frequently on returns that come to us for second opinions or after a state notice arrives:

• Accepting the brokerage's state apportionment without checking. Brokerage supplemental statements often show 100% California apportionment for all RSU vests, even if the employee spent years working in other states during the grant period. This overstates California income.
• Forgetting the other state's nonresident return. If you worked in New York for a week on a business trip and New York has a tax treaty with your employer's payroll, you may have New York nonresident filing obligations. Many taxpayers ignore small nonresident state obligations that compound into audit triggers.
• Incorrect Schedule S computation. The credit is limited in ways that many software programs compute incorrectly, especially when multiple states are involved. We manually verify the Schedule S calculation.
• Missing the California-source tail after leaving the state. Former California residents stop thinking about California taxes as soon as they move. But unvested RSUs granted while in California continue to generate California-sourced income on each vest date until the full grant-to-vest period shifts to the new state.
• Misclassifying the move date. California uses the last day you left California as your California resident period end date. If you moved in December but were still in California until December 20, your California resident period includes all income earned through December 20, not through November 30 when you signed the new lease.

Our Office and Engagement Process

Silicon Valley Tax is located at 2051 Junction Ave Suite 200, San Jose CA 95131. We handle multi-state returns for clients throughout the Bay Area and work with clients virtually across the country who have California-sourced income from equity compensation, rental property, or business activities.

Multi-state returns take more time than single-state returns because of the sourcing analysis and the ordered preparation of returns. We typically begin multi-state return engagements earlier in tax season to allow time for state-level questions and to ensure other-state returns are completed before the California Schedule S is finalized.

Call (408) 383-9870 or use the online booking form to schedule a free consultation. If you have already received a notice from California or another state, bring that too. Post-audit cleanup is one of the most common entry points for new multi-state clients.

Frequently Asked Questions About Multi-State Tax Returns

I work remotely in California for a New York employer. Which states tax my wages?

California taxes all your wages because you are a California resident performing services from California. New York may also assert tax under its convenience of the employer doctrine, claiming your wages are New York-sourced unless your remote arrangement is a business necessity required by the employer. California provides a credit for taxes paid to New York on Schedule S, but the credit may not fully eliminate the double taxation if California's effective rate is lower than New York's. We evaluate the employer necessity argument and model both tax outcomes before filing.

How are RSUs taxed when I move from California to another state mid-vesting?

RSUs are sourced proportionately to where you worked during the period from grant date to vest date. California workdays during the grant-to-vest period divided by total workdays equals the California apportionment fraction. That fraction multiplied by the total vest income equals California-sourced income. If you were in California for two of three years in a vesting period, roughly two-thirds of the vest is California-sourced, even if you are now living in another state. We track and compute this apportionment for each RSU tranche separately.

What is the credit for taxes paid to other states on a California return?

California Schedule S credits you for income taxes paid to another state on income also taxed by California. The credit is limited to the lesser of what California would tax on that income (at California's rate) or what you actually paid to the other state. If both states want the same dollar of income, this credit significantly reduces but may not fully eliminate the double taxation. We compute Schedule S manually to verify that software-generated amounts are correct, especially when multiple states are involved.

I moved from California to another state during the year. Do I owe California tax on income I earned after I left?

You owe California tax on income earned while you were a resident, and on California-sourced income earned after you left. California-sourced income includes wages for services performed in California, RSU vest income apportioned to California days during the grant period, and gain from selling California real estate. Income from a new job in your new state, performed entirely from the new state after departure, is not California-sourced. The analysis depends on the move date and the specific income types.

My company is headquartered in Washington state. I live in San Jose and work entirely from home. Do I still owe California tax?

Yes. California taxes wages earned while you are a California resident performing services from California, regardless of where your employer is headquartered. Washington has no state income tax, so there is no second state claiming your wages. This is actually a cleaner situation than having a New York or Massachusetts employer: you pay California tax on your wages, but there is no double taxation or convenience doctrine issue. Only California applies here for your wage income.

Related Services

For more on equity compensation sourcing, see our pages on equity compensation tax and AMT tax planning. For city-specific coverage, see our pages for San Jose tax accountant and Palo Alto tax accountant. If your multi-state situation involves a business, see our pages on entity tax and CFO advisory services.