State income tax apportionment is the process each state uses to tax only its fair slice of a multistate company’s income. When your business earns revenue across state lines, every state where you have sufficient contact applies its own formula, measuring how much of your activity happens inside its borders and taxing only that percentage of your total income. The formulas differ, but the principle is uniform: a state’s share of the tax should reflect the share of business actually conducted there.
What follows is a working guide to how those formulas operate, when a state can reach your income in the first place, and the rules that quietly swing the result by millions of dollars for larger filers.
When a State Can Reach Your Income
Before any formula applies, a state must establish that your company has “nexus” there. Historically, nexus required a physical footprint: an office, a warehouse, employees traveling through. That standard has stretched. Many states now assert income tax nexus on economic activity alone, through a concept called factor presence.
Under the Multistate Tax Commission’s model standard, a company creates nexus if it exceeds any one of these thresholds during a tax year:
- $50,000 in property located in the state
- $50,000 in payroll paid in the state
- $500,000 in sales sourced to the state
- 25 percent of the company’s total property, payroll, or sales
Several states have adopted these thresholds or variations; others set their own numbers.1Multistate Tax Commission. Factor Presence Nexus Standard for Business Activity Taxes The practical result: a company with no physical presence can still owe corporate income tax in a state if its sales there are large enough. Remote sellers and digital businesses carry the heaviest compliance load.
One federal statute pushes back. Public Law 86-272 bars a state from imposing a net income tax on a company whose only in-state activity is soliciting orders for tangible personal property, provided those orders are approved and filled from outside the state.2Office of the Law Revision Counsel. United States Code Title 15 Section 381 The shield is narrow. It covers tangible goods, pure solicitation, and nothing else. Companies selling services, licensing software, or doing anything digital beyond basic solicitation fall outside it.
How the Formula Works
Once nexus exists, the state applies its apportionment formula to produce a percentage. Multiply your total business income by that percentage, and you have the amount the state can tax.
The traditional formula comes from the Uniform Division of Income for Tax Purposes Act (UDITPA), a 1950s model law that gave states a common approach. UDITPA uses three equally weighted factors: property, payroll, and sales. Each factor compares in-state activity to activity everywhere, giving a fraction. Average the three fractions to get the apportionment percentage.
Equal weighting is now the minority approach. About two-thirds of states with a corporate income tax use a single sales factor formula, which ignores property and payroll and bases the entire percentage on where the company’s customers are located.3Multistate Tax Commission. Review of MTC Model Sales Receipts Sourcing and Special Industry Regulations Some states use a weighted formula that emphasizes sales but still gives smaller weight to property and payroll. Only about 10 percent of taxing states still apply the original equally weighted three-factor approach.
The shift to a single sales factor is deliberate policy. When property and payroll count, building a factory or hiring in a state raises that state’s apportionment percentage and the tax bill. Removing those factors eliminates the disincentive and tells companies they can invest and hire locally without a tax penalty. The trade-off is that states with large consumer markets pull more revenue from out-of-state sellers, while states that primarily host manufacturing or back-office work lose base.
What Each Factor Measures
Even in single-sales-factor states, the other two factors can matter for nexus determinations and for returns filed in states that still weight them.
Property
The property factor compares the value of real estate and tangible business property in the state to total property everywhere. Under UDITPA, property is valued at original cost, not depreciated book value. Rented property is converted to an ownership-equivalent value by multiplying net annual rent by eight.4Multistate Tax Commission. Multistate Tax Compact The factor averages beginning-of-year and end-of-year values.
Payroll
The payroll factor compares compensation paid to employees working in the state to total compensation paid everywhere. Compensation covers wages, salaries, commissions, and other remuneration. For an employee who works in multiple states, pay is generally assigned to the state where the employee’s base of operations sits or where the work is directed and controlled.
Sales
The sales factor compares revenue sourced to the state against total revenue everywhere. For physical products, sourcing is simple: the sale lands wherever the goods are delivered. For services and intangibles, sourcing is where most of the complexity, and most of the money, now sits.
Sourcing Sales: Where the Revenue Lands
Sourcing rules decide which state gets credit for each sale. The fight is over services and intangible property, where two competing methods have shaped state tax policy for decades.
Cost-of-Performance
The older method assigns a service sale to the state where the company incurs the costs of delivering it. If a consulting firm does most of the work from its headquarters in State A, the fee for a client in State B is sourced to State A. When costs split across states, the whole sale typically goes to the state with the largest share of costs. That all-or-nothing treatment created obvious planning: concentrate your service workforce in a low-tax state, source most of your revenue there.
Market-Based Sourcing
The majority of taxing states have moved to market-based sourcing, which assigns service revenue to the state where the customer receives the benefit.3Multistate Tax Commission. Review of MTC Model Sales Receipts Sourcing and Special Industry Regulations A New York law firm advising a Texas client sources that fee to Texas under market-based rules. The theory is that income comes from the market, not the back office.
Market-based sourcing works cleanly for identifiable services and gets messy fast with digital products. Where is the “benefit received” when a company licenses software accessible nationwide, or sells digital advertising viewed across dozens of states? Software licensing revenue often follows the user’s access location, which can require tracking logins. Digital advertising tends to follow the audience, split by the share of viewers in each state. Methodology still varies state to state.
Financial institutions, airlines, railroads, and trucking companies often apportion income using industry-specific factors such as deposits, revenue miles, or originated loans rather than the general sales factor.
Business Income vs. Non-Business Income
Not every dollar runs through the apportionment formula. States following UDITPA split corporate income into two buckets, and only business income gets apportioned.
Business income arises from the company’s regular operations or from property integral to those operations. If a manufacturer sells a warehouse it has used for years, the gain is business income because the warehouse was part of the ongoing enterprise. Non-business income is everything else, typically passive investment returns disconnected from operations, like interest on a short-term bank deposit or rent from property held purely for investment.
Non-business income is allocated rather than apportioned, meaning it goes entirely to one state. Under UDITPA’s model rules:
- Real property rents, royalties, and gains are allocated to the state where the property sits.
- Tangible personal property rents and gains are allocated to the state of use, or to the company’s commercial domicile if the company isn’t taxable in the state of use.
- Interest and dividends are allocated to the state of commercial domicile.
- Patent and copyright royalties are allocated to the state where the payer uses the right.
Commercial domicile is generally the company’s principal place of business.5Multistate Tax Commission. UDITPA Issues to Consider for Revision Classification matters because labeling income as non-business can shift where it is taxed. States tend to read business income broadly, often applying both a transactional test (earned in the regular course of business?) and a functional test (property integral to operations?) to pull as much as possible into the apportionment formula.
Combined Reporting and Related Entities
Large corporations often operate through networks of subsidiaries, and how a state treats those entities can change the apportionment result dramatically.
Under separate entity reporting, each subsidiary files on its own. Only subsidiaries that individually have nexus with the state file and pay tax there. This opens planning doors: shift income to a subsidiary incorporated in a low-tax or no-tax state and the overall burden drops.
Under combined reporting, all members of a “unitary” group pool their income and apportion it together. A unitary group exists when the subsidiaries are sufficiently integrated that the operations of one contribute to the profitability of the others. Roughly half the states with a corporate income tax now require combined reporting, mostly to shut down the income-shifting that separate filing allows.6Institute on Taxation and Economic Policy. Combined Reporting of State Corporate Income Taxes A Primer
Multinationals face a second question: which affiliates get pulled in? A water’s-edge election excludes foreign subsidiaries and certain U.S. entities doing most of their business overseas. Worldwide combined reporting includes every affiliate everywhere. Most states defaulting to combined reporting apply water’s-edge or allow companies to elect it.
Joyce vs. Finnigan
When a combined group files in a state, a secondary question arises: what happens to sales made into that state by a group member that doesn’t individually have nexus there? Two rules compete.
Under the Joyce approach, only sales by group members that individually have nexus count in the state’s sales factor numerator. If Subsidiary A has nexus in Minnesota but Subsidiary B does not, Minnesota ignores Subsidiary B’s sales when calculating the group’s apportionment percentage. Under the Finnigan approach, the combined group is treated as a single taxpayer. If any member has nexus, all members’ sales into the state count in the numerator.7Multistate Tax Commission. Finnigan Briefing Book Finnigan generally produces a higher apportionment percentage and a larger tax bill, which is why revenue-hungry states tend to prefer it.
Throwback and Throwout Rules
Apportionment can leave gaps where income isn’t taxed by any state. The classic case: a company ships goods from State A to customers in State B, but has no nexus in State B. State B can’t tax the income. State A might not include the sale in its own numerator because the goods were delivered elsewhere. The revenue falls into a “nowhere” category. Throwback and throwout rules close that gap.
Throwback
About twenty-two states and the District of Columbia use a throwback rule. When a company ships tangible goods from the state into a destination state where it isn’t taxable, the sale is thrown back and included in the originating state’s sales factor numerator.8Multistate Tax Commission. Notes on Throwback Rule Ship from Illinois to a customer in a state where you have no nexus, and Illinois counts the sale as an Illinois sale for formula purposes. Throwback applies only to tangible personal property.
Throwout
A smaller number of states use a throwout rule. Rather than adding nowhere sales to the numerator, throwout removes them from both the numerator and denominator. The apportionment percentage still rises because the denominator shrinks. States using throwout tend to apply it more broadly than throwback, sometimes to intangibles and services as well as tangible goods.
Both rules depend on whether the company is “taxable” in the destination state, and that determination often turns on P.L. 86-272. If the only destination-state activity is soliciting orders for tangible goods, the federal shield makes the company not taxable there, which triggers throwback or throwout at the origin.2Office of the Law Revision Counsel. United States Code Title 15 Section 381 If activities go beyond pure solicitation, the shield drops, the destination state can tax, and the origin state’s throwback no longer bites.
P.L. 86-272 and Website Activity
P.L. 86-272 was written in 1959, when interstate commerce meant shipping physical goods. Its protection covers only companies whose sole in-state activity is soliciting orders for tangible personal property. It has never covered services, digital products, licensing, or anything intangible.2Office of the Law Revision Counsel. United States Code Title 15 Section 381
The Multistate Tax Commission has issued revised guidance identifying common internet activities that strip P.L. 86-272 protection even for companies selling tangible goods. Activities that exceed protected solicitation include:
- Post-sale customer support via live chat or email initiated through the company’s website
- Online branded credit card applications, which generate separate interest and fee income
- Allowing in-state job applicants to submit applications and resumes online
- Placing tracking cookies on in-state customers’ devices to collect browsing data used for product development, inventory planning, or targeted marketing
- Transmitting software fixes or upgrades to products already purchased by in-state customers
- Offering and selling extended warranty plans through the website
Any of these can create nexus in every state where customers interact with the website.9Multistate Tax Commission. Statement of Information Concerning Practices of Multistate Tax Commission and Supporting States Under Public Law 86-272 For e-commerce sellers that once relied on P.L. 86-272, these interpretations substantially expand state taxing authority. A business that only ships physical products but uses its website for customer data or support may now owe income tax in states it previously ignored.
Who Apportionment Applies To
Apportionment primarily affects C-corporations operating in more than one state. S-corporations, partnerships, and LLCs taxed as pass-throughs generally don’t pay corporate income tax at the entity level; income flows through to individual owners who report it on their personal state returns. A growing number of states now allow pass-through entity taxes, where the entity itself pays state tax on behalf of its owners, and apportionment formulas can apply to those elections too.
Six states impose no corporate income tax at all. Nevada, Ohio, Texas, and Washington levy gross receipts taxes instead, while South Dakota and Wyoming impose neither. Companies operating exclusively in those states don’t face apportionment for corporate income tax purposes, though gross receipts taxes carry their own sourcing rules.