What Is California Source Income and How Is It Taxed?

California source income is any income the state’s Franchise Tax Board can trace to work performed inside California, property located there, services whose benefit is received there, or an interest in a California business. If you live in California all year, this concept barely matters because you owe California tax on everything you earn worldwide. If you live elsewhere, it matters a great deal: it decides the entire California tax bill.¹

Who Actually Owes California Tax on It

Three categories of taxpayers encounter the rule differently. Full-year residents pay California tax on all income from every source, so sourcing is irrelevant to them. Non-residents pay California tax only on California source income. Part-year residents pay on everything they received during the months they lived in California, plus any California source income they received during the months they lived somewhere else.¹

Residency itself turns on domicile and physical presence. More than nine months in California during a tax year creates a presumption of residency that is hard to rebut.² If you are domiciled outside California, keep a permanent home at that out-of-state domicile, limit your California time to six months or less, and confine your California activity to that of a visitor, you qualify for a safe harbor that treats your presence as temporary. Regular business activity in the state can break that safe harbor even if you stay under six months.³

What Counts, by Type of Income

Wages and Salary

For employees, wages are sourced to where you physically perform the work, not where your employer is located. A non-resident working remotely from Texas for a San Francisco employer has no California source wages. A non-resident who flies into Los Angeles for a week of meetings does.¹

The FTB uses a duty-days ratio to split pay: California workdays divided by total workdays, multiplied by annual compensation. Someone earning $200,000 who works 20 of 250 workdays in California has $16,000 of California source wages. Bonuses and commissions tied to those services are prorated the same way.¹

Independent Contractor and Self-Employment Income

The sourcing rule flips for independent contractors. Your income is sourced to where the customer receives the benefit of your services, not where you perform the work.¹ A freelance developer in Oregon who builds a website for a Los Angeles client has California source income even though no work was performed in California. A consultant physically in California whose client receives the benefit in New York may have none from that engagement. The FTB looks to contract terms and billing records; the customer’s billing address is the default presumption when nothing else answers the question.⁴

Stock Options and RSUs

Equity compensation granted while you worked in California still generates California source income after you move, even if you exercise or vest in a state with no income tax. For non-qualified stock options, the FTB allocates income using the ratio of California workdays to total workdays between grant and exercise. For restricted stock and RSUs, the period runs from grant to vesting. If employment ends first, the period ends then.⁵

If you were granted options while in California, worked three of the four years between grant and exercise in California, then moved to Washington and exercised, roughly 75% of the option income remains California source. People leaving for tax-free states often learn this after the fact.

Real Property

Income tied to real estate physically located in California is always California source income, no matter where you live. Rent from a San Diego apartment, royalties from a Kern County mineral deposit, and timber income from Northern California land are all fully taxable by the state. Capital gain on the sale of a Palm Springs vacation home is 100% California source, regardless of where the sale was negotiated or closed.

Stocks, Bonds, and Other Intangibles

Gains from selling stocks, bonds, mutual funds, and other intangible personal property generally follow your state of residence and are not California source income for non-residents.⁶ A non-resident selling shares of a California-headquartered public company typically owes no California tax on the gain. Two exceptions change the result:

Business situs. If the intangible has acquired a connection to a California trade or business — a partnership interest used in a business operating primarily in California is the classic example — the gain is California source.
Regular trading in California. Buying and selling securities through California brokers so regularly and systematically that it amounts to doing business in the state makes those profits California source.⁶

Non-resident partners selling a partnership interest face a further trap. Under FTB Legal Ruling 2022-02, the portion of your gain attributable to the partnership’s appreciated inventory or unrealized receivables is treated as business income apportioned to California using the partnership’s own apportionment formula, rather than as a simple intangible sale sourced to your residence.

Retirement Income

Federal law bars states from taxing qualified retirement income received by non-residents. The shield covers distributions from 401(k) plans, traditional and Roth IRAs, 403(b) plans, 457 plans, SEP-IRAs, and government pensions.⁷ If you retired from a California employer and moved to Nevada, your pension is not California source income.

The shield does not cover everything deferred. Non-qualified deferred compensation and certain severance payments fall outside federal protection, and California can source that income back to the state based on where you performed the underlying services, using the same duty-days approach that applies to wages.

Business Income From Multi-State Operations

When a non-resident earns business income from a multi-state operation, California takes only its apportioned share. Most businesses use a single-sales-factor formula: only the proportion of sales attributable to California determines California’s share of business income. Agriculture, extractive industries, and banking use a three-factor formula weighting property, payroll, and sales equally.⁸

The sales factor uses market-based sourcing. Physical goods are sourced to California when delivered to a California buyer. Services are sourced to California to the extent the customer receives the benefit there. Patent royalties are sourced to California when the licensee uses the patent to manufacture within the state. For individual customers, the billing address is the default. For business customers, the FTB looks to contract terms and business records first, falling back on the location from which the customer placed the order.⁴

How California Calculates the Tax on It

California does not simply drop your California source income into its lowest brackets. The state uses a proration that effectively taxes that income at the marginal rate your worldwide income would command. The calculation runs in three steps:

Calculate the tax you would owe as a full-year California resident on all your worldwide income.
Divide that tax by your total taxable income to get an effective rate.
Multiply your California taxable income by that effective rate.⁹

If your worldwide income is $500,000 and your California source income is $100,000, you pay tax on the $100,000 at the rate someone earning $500,000 would face, not the rate on $100,000 in isolation. The difference matters given California’s steeply progressive brackets. Deductions and credits are prorated the same way: your California AGI divided by your total AGI sets the share of your itemized or standard deduction you can use.⁹

Withholding That Happens Before You File

Real Estate Sales

Non-residents selling California property face an immediate cash hit. The buyer must withhold 3⅓% of the total sales price and send it to the FTB. The requirement does not apply when the sales price is $100,000 or less, and the seller can elect an alternative amount equal to the estimated gain multiplied by the highest applicable tax rate, which can come out lower than 3⅓% of gross price. The withholding also does not apply in several situations:¹⁰

The property qualifies as your principal residence under federal Section 121 rules.
Gain is deferred in a Section 1031 like-kind exchange, to the extent of the deferral.
The transaction produces a loss, or no gain is recognized for California tax purposes.

The withholding is a prepayment, not an extra tax. You claim credit for it on your non-resident return and receive a refund if it exceeded your actual liability.¹⁰

Pass-Through Entities

If you are a non-resident partner, LLC member, or S corporation shareholder in a California pass-through entity, the entity generally must withhold on your share of California source income and remit quarterly on Form 592-Q. The entity reconciles those payments on Form 592-PTE by January 31 of the following year. Again, a prepayment, not an additional tax.¹¹

Filing the Return and Paying Estimates

Non-residents and part-year residents file Form 540NR. For the 2025 tax year, a single non-resident under 65 with no dependents must file if gross income from all sources exceeds $22,941. For a married couple filing jointly, both under 65 with no dependents, the threshold is $45,887 of combined gross income. Thresholds rise with age and number of dependents.¹² Even below the threshold, file if California tax was withheld, so you can recover the refund.

Estimated payments are required if you expect to owe $500 or more after withholding and credits ($250 if married filing separately).¹³ California’s schedule is not four equal installments. It is 30%, 40%, nothing, 30%:

April 15 — 30% of the annual estimate.
June 15 — 40%.
September 15 — no payment due.
January 15 of the following year — the remaining 30%.¹³

You avoid an underpayment penalty if your payments and withholding cover at least the lesser of 90% of this year’s tax or 100% of last year’s California liability, including alternative minimum tax. Non-residents who had no California liability in the prior year owe no estimates.¹⁴ California does not give non-residents a credit for tax paid to another state on California source income; the credit for taxes paid to California comes from your home state’s return.

What Happens If You Ignore It

The FTB charges a delinquent filing penalty of 5% of the unpaid tax per month or partial month, capped at 25%. If the FTB sends a Demand for Tax Return and you still do not file, a flat 25% penalty on the total tax due is added on top.¹⁵ Late payment carries its own penalty: 5% of unpaid tax plus 0.5% for each month unpaid, up to 40 months of the monthly piece. Interest accrues on top at 7% per year.¹⁶

The FTB generally has four years from the later of the original due date or the date you filed to assess additional tax. Omit more than 25% of your gross income and the window stretches to six years. Never file a California return at all, and no statute of limitations applies — the FTB can assess at any time.¹⁷ That last rule is the one that catches non-residents. People with California rental property, pass-through K-1s, or vested equity from a past California job sometimes assume no return is needed because they live elsewhere. If the FTB disagrees years later, the assessment clock never started.

A Note for Military Spouses

The federal Military Spouses Residency Relief Act carves out an exception. If you are legally married to an active-duty servicemember stationed in California on military orders and you moved to California solely to be with them, your wages earned in California are not California source income. File a DE 4 with your employer to stop California income tax withholding. The wages remain subject to California unemployment and disability insurance because the work physically happens in the state. If California income tax was already withheld before you filed the DE 4, claim it back on your state return.¹⁸

1
Franchise Tax Board. Part-Year Resident and Nonresident
2
California Legislative Information. California Revenue and Taxation Code 17016
3
Legal Information Institute. California Code of Regulations 18 CCR 17014 – Who Are Residents and Nonresidents
4
Legal Information Institute. California Code of Regulations 18 CCR 25136-2 – Sales from Services and Intangibles
5
Franchise Tax Board. Residency and Sourcing Technical Manual
6
California Legislative Information. California Revenue and Taxation Code 17952
7
Office of the Law Revision Counsel. 4 U.S. Code 114 – Limitation on State Income Taxation of Certain Pension Income
8
Franchise Tax Board. Apportionment and Allocation
9
Franchise Tax Board. FTB Publication 1100 – Taxation of Nonresidents and Individuals Who Change Residency
10
California Legislative Information. California Revenue and Taxation Code 18662
11
Legal Information Institute. California Code of Regulations 18 CCR 18662-8 – Reporting and Remitting
12
Franchise Tax Board. 2025 Instructions for Form 540NR Nonresident or Part-Year Resident Booklet
13
Franchise Tax Board. Estimated Tax Payments
14
Franchise Tax Board. 2025 Instructions for Form 540-ES
15
Franchise Tax Board. Common Penalties and Fees
16
Franchise Tax Board. Interest and Estimate Penalty Rates
17
Franchise Tax Board. Manual of Audit Procedures – Chapter 4, Statute of Limitations and Waivers
18
Employment Development Department. Military Spouses Residency Relief Act