Tax
Multi-State Apportionment
The formula that divides your business income among the states you operate in so each one taxes only its share.
Once your business has nexus in more than one state, you cannot pay income tax on 100% of your profit to every state — that would be double taxation. Apportionment is the mechanism each state uses to figure out what percentage of your total income belongs to it.
Most states now use a single-sales-factor formula: the percentage of your total sales that were sourced to that state equals the percentage of income the state taxes. A handful still use a three-factor formula that averages sales, payroll, and property. Sourcing rules differ too: some states source service revenue to where the customer received the benefit, others to where the work was performed.
For an owner-led service business, apportionment shows up the moment you take on clients across state lines, hire a remote employee, or open a second location. The state where you are legally organized still gets to tax you on income not apportioned elsewhere.
Common pitfalls
- Assuming your home state gets 100% of your income when you clearly serve clients in other states — this is a common audit finding
- Using different sourcing rules than each state requires, which quietly overpays some states and underpays others
- Ignoring economic-nexus thresholds — you can owe income tax filings in states you never physically set foot in
- Forgetting that PTE elections and credit-for-taxes-paid rules interact with apportionment; the coordination matters at the owner level
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