Toolkit · Tax

The Nexus Study, Apportionment Model, and Unitary Analysis Toolkit

15 U.S.C. § 381

Type
Toolkit
Jurisdiction
National
Date
2024-10-17
Topic
Tax

This toolkit supplies the working documents for multistate tax practice. It opens with the contact inventory grid and the tax type matrix, since nexus must be determined state by state and levy by levy and a conclusion for one tax does not carry to another. The solicitation audit tests the narrow federal protection against what personnel actually do. The unitary file and the sourcing methodology document are the two records that decide most examinations, and both must be built contemporaneously. Later instruments cover the exposure model, the voluntary disclosure analysis, the throwback model, the combined reporting comparison, the assessment defense outline, the internal consistency test, the remote employee register, and the diligence request list for transactions.

The Nexus Study, Apportionment Model, and Unitary Analysis Toolkit

Tax > State Tax Nexus, Apportionment, and Combined Reporting | Published 17 October 2024 - Updated 12 May 2026 | UpLaw - uplaw.us

Instrument 1: the contact inventory grid

Purpose. To establish, state by state, what connections exist.

Rows. Each state and, where local taxes apply, each relevant locality.

Columns. Property owned. Property leased. Employees, with count and function. Remote workers. Independent contractors and representatives. Inventory, including at third-party fulfillment providers. Sales volume. Transaction count. Registrations and licenses. Deliveries in company vehicles. Installation, training, repair, or warranty activity. Trade show attendance and its duration. Bank accounts and financing relationships.

Sources. Payroll records by work location rather than by assignment. Fixed asset registers. Lease schedules. Third-party logistics agreements. Sales data by ship-to address. Contractor agreements and what the contractors actually do.

Discipline. Build from records rather than from management's understanding, since the two frequently differ and the records are what an examiner will see.

Instrument 2: the tax type matrix

Purpose. To prevent the most common analytical error — concluding nexus for one tax and assuming it for all.

Rows. Sales and use tax collection. Corporate income tax. Gross receipts tax. Franchise tax. Employment tax and withholding. Local levies.

Columns. The state's standard for each. Whether the threshold is met. Whether the federal protection in 15 U.S.C. § 381 is available, noting that it reaches only net income taxes as defined in 15 U.S.C. § 383. The registration requirement. The filing frequency. The date the obligation began.

Framework. Complete Auto Transit, Inc. v. Brady supplies the constitutional test, and South Dakota v. Wayfair, Inc. supplies the current nexus standard, having overruled National Bellas Hess, Inc. v. Department of Revenue and Quill Corp. v. North Dakota ex rel. Heitkamp.

Attribution. Where activities are conducted by others on the taxpayer's behalf, apply Tyler Pipe Industries, Inc. v. Washington State Department of Revenue, asking whether they are significantly associated with the ability to establish and maintain a market.

Instrument 3: the solicitation audit

Purpose. To test reliance on the federal protection against what personnel actually do.

Method. For each employee or representative in a state where the protection is claimed, list every activity performed, from expense reports, calendars, call logs, and interviews — not from job descriptions.

Protected. Solicitation of orders for sales of tangible personal property, sent outside the state for approval or rejection and filled from outside, together with activities ancillary to solicitation.

Unprotected. Installation. Training. Repair and warranty work. Credit investigation and collection. Inventory maintenance. In-state approval of orders. Technical assistance beyond solicitation support. Providing engineering services. Maintaining a sample or display room beyond permitted periods.

Categorical exclusions. Services, intangibles, and leasing fall outside the protection entirely, regardless of the activity's character.

Output. A per-state conclusion with the supporting activity list, since the protection is claimed on a return and will be tested on audit.

Instrument 4: the unitary file

Purpose. To document the determination that decides what income enters the apportionable base.

Contents. Organizational charts across the relevant years. Intercompany agreements and evidence of their actual operation. Shared service arrangements with their scope and pricing. Board and committee minutes showing where strategic decisions are made. Officer and director overlap with actual roles. Employee movement among entities. Common systems, branding, and customer relationships. Financing arrangements and guarantees. Intercompany transaction volumes.

The indicia to address, drawn from Container Corp. of America v. Franchise Tax Board: functional integration, centralization of management, and economies of scale.

Points to anticipate. That internal accounting divisions do not establish separateness, per Exxon Corp. v. Department of Revenue of Wisconsin. That ownership and dividends do not establish unity, per ASARCO Inc. v. Idaho State Tax Commission and F.W. Woolworth Co. v. Taxation and Revenue Department of New Mexico. That the operational function concept describes when an asset is part of the unitary business rather than supplying an independent ground, per MeadWestvaco Corp. v. Illinois Department of Revenue clarifying Allied-Signal, Inc. ex rel. Bendix Corp. v. Director, Division of Taxation.

Consistency log. Positions taken on unity by state and year, since inconsistency is used against taxpayers and departments alike.

Instrument 5: the sourcing methodology document

Purpose. To record, contemporaneously, how receipts are assigned — the most valuable document in an income tax audit.

Structure. One section per revenue stream.

Contents per stream. The nature of the receipt. The applicable rule in each state — destination, cost of performance, or market-based with its cascading provisions. The data used to apply the rule, and its source. The determination reached. Any known ambiguity and how it was resolved. The date and the person responsible.

For tangible personal property. Destination sourcing, with throwback or throwout applied where the destination state cannot tax — noting that receipts protected by 15 U.S.C. § 381 in the destination state may be thrown back to the origin state.

For services and intangibles. Where the benefit is received, determined under each state's cascade, with the specific data point identified.

Why contemporaneous. The audit asks why receipts were assigned as they were, and an answer constructed years later is worth a fraction of one recorded at the time.

Instrument 6: the apportionment model

Purpose. To compute liability under each state's actual rules rather than under a uniform assumption.

Structure. One column per state, with rows for each factor and each adjustment.

Rows. Property factor numerator and denominator, with valuation method. Payroll factor numerator and denominator, with assignment rules. Sales factor numerator and denominator, sourced under Instrument 5. Factor weighting. Apportionment percentage. Apportionable base after unitary determination. Allocable income assigned to specific states. Tax rate. Credits. Liability.

Throwback and throwout modeling. Where sales to a state cannot be taxed there, whether they are thrown back to the origin state or thrown out of the denominator, and the effect of establishing nexus in the destination state on that treatment.

Sensitivity analysis. Aggregate apportionment across all states, noting that it need not equal one hundred percent — Moorman Manufacturing Co. v. Bair holds that overlap among differing formulas is a matter for Congress.

Alternative scenarios. The effect of hiring in a new state, of a new inventory location, or of a change in sourcing methodology.

Instrument 7: the combined reporting comparison

Purpose. To test a structure under both regimes before adopting it.

Columns. States requiring combined reporting. States permitting or requiring separate reporting. States with add-back statutes.

Rows. The group's income by entity. Intercompany transactions and their treatment. Factors by entity. The resulting apportionment and liability under each regime.

Points to model. Whether combination eliminates the benefit of an intercompany structure entirely. Whether add-back statutes reach the transaction and whether an exception applies because the recipient was subject to tax elsewhere. Whether the combination scope is water's edge or worldwide, noting that worldwide combination is permitted under Container Corp. of America v. Franchise Tax Board and Barclays Bank PLC v. Franchise Tax Board of California, and whether an election is available.

The risk to flag. A structure producing a benefit in some states while supporting a department's argument for forced combination or alternative apportionment in others.

Instrument 8: the exposure model

Purpose. To quantify unfiled and underpaid liability before choosing a remediation route.

Rows. Each state and each year.

Columns. Tax type. Whether a return was filed. The liability computed. Interest to date. Penalties. Whether the limitations period has run, recognizing that periods generally run from filing so unfiled years remain open.

Aggregation. Total exposure, and exposure by state, so that remediation can be prioritized.

Sensitivity. The effect of alternative nexus start dates and alternative sourcing positions, since both are contestable.

Instrument 9: the voluntary disclosure analysis

Purpose. To evaluate the remediation options.

For each state. Whether a voluntary disclosure program exists. The look-back period it offers. Whether penalties are waived. Whether interest is reduced. Whether anonymity is available during negotiation. Whether the program is foreclosed by prior contact from the state.

Comparison. Exposure under the program against exposure if assessed, including the value of a limited look-back where periods would otherwise be open indefinitely.

Alternatives. Amnesty programs where available. Prospective registration, which addresses the future without resolving the past and which can invite inquiry.

Timing discipline. Voluntary disclosure is generally unavailable once the state initiates contact, which makes the decision time-sensitive and argues against deferral.

Instrument 10: the assessment defense outline

Purpose. To organize a protest in order of the defenses' strength.

Section one — nexus. Whether the state's standard was satisfied in each year, and whether 15 U.S.C. § 381 protects against a net income tax, with the solicitation audit from Instrument 3 attached.

Section two — the apportionable base. Whether the income included is unitary under Mobil Oil Corp. v. Commissioner of Taxes of Vermont and Container Corp. of America v. Franchise Tax Board, or falls outside under the boundary cases, with the unitary file from Instrument 4 attached.

Section three — the formula. Factor computation and receipts sourcing, with the methodology document from Instrument 5 attached, and the burden acknowledged as heavy after Moorman Manufacturing Co. v. Bair.

Section four — internal consistency, following Comptroller of the Treasury of Maryland v. Wynne, asking whether the scheme would produce multiple taxation if adopted universally.

Section five — discrimination in operation as well as form.

Section six — alternative apportionment, where the standard formula does not fairly represent the taxpayer's activity.

Section seven — penalties, supported by evidence of a reasoned contemporaneous determination.

Procedural checklist. Protest deadline, administrative appeal requirements, payment-under-protest rules, and judicial review availability, each of which varies by state and is strictly applied.

Instrument 11: the internal consistency test

Purpose. To apply the analytical tool that isolates a scheme's discriminatory effect.

Method. Hypothesize that every state adopted the challenged scheme. Compute the total tax borne by a purely intrastate taxpayer and by an otherwise identical interstate taxpayer.

The conclusion. If the interstate taxpayer bears more solely because of the interstate character of its activity, the scheme is internally inconsistent and discriminates against interstate commerce, as Comptroller of the Treasury of Maryland v. Wynne holds.

What the test does not reach. Overlap arising because different states use different but internally consistent formulas, which Moorman Manufacturing Co. v. Bair leaves to Congress.

Documentation. Show the computation, since the argument is quantitative and a court will want the arithmetic rather than the assertion.

Instrument 12: the remote employee register

Purpose. To track the fact that most often creates unexpected obligations.

Columns. Employee. Home state and locality. Percentage of time worked there. Function performed. Whether the function is limited to solicitation of orders for tangible personal property. Date the arrangement began. Whether the state has been registered. Withholding treatment. Whether any convenience rule applies.

Trigger. Any new remote arrangement prompts a nexus and withholding review before the arrangement begins.

Consequences to model. Income tax nexus, since 15 U.S.C. § 381 rarely protects remote work. Payroll factor shifts. Withholding obligations. And the elimination of throwback on sales to that state, which can reduce liability in the origin state.

Instrument 13: the transaction diligence request list

Purpose. To identify state tax exposure in an acquisition.

Requests. Returns filed by state and year for every tax type. Nexus studies or memoranda. Employee locations by year. Inventory locations including third-party facilities. Sales by ship-to state by year. Exemption certificate files. Taxability determinations and their bases. Apportionment workpapers with sourcing support. Intercompany agreements. Audit history, assessments, and appeals. Voluntary disclosure agreements. Bulk sale or clearance certificates.

Analysis. Compare the filing footprint against the contacts, since unfiled states are the principal risk and their periods do not close.

Structure consequences. A stock acquisition carries the history; an asset acquisition may not, subject to successor liability provisions that many states impose for transaction taxes.

Deal terms. Representations, indemnity sized to identified exposure, escrow, clearance certificate covenants, and a covenant to pursue voluntary disclosure where unfiled exposure exists.

How the instruments sequence

Instruments 1 through 3 come first and answer where obligations exist. They take days and they are the foundation of everything else.

Instruments 4 and 5 are the ongoing discipline, built contemporaneously because both record facts that cannot be reconstructed persuasively.

Instruments 6 through 9 quantify and remediate, and Instrument 9 is time-sensitive because voluntary disclosure closes on contact.

Instruments 10 and 11 are the defense, and their strength depends entirely on whether Instruments 3 through 5 were maintained.

Instruments 12 and 13 address the two events that most often create new exposure: a remote hire and an acquisition.

Instrument 14: the transaction tax compliance file

Purpose. To manage the exposure that accrues fastest, since transaction tax liability is measured on gross receipts rather than on income.

Taxability matrix. Each product and service line by state, with the determination, the statutory or regulatory basis, and the date reviewed. Software, digital goods, information services, and bundled offerings require particular attention, since treatment varies and a single product may be taxable in some states and not others.

Rate and address determination. Destination sourcing with local taxes requires accuracy below the state level, and the method used should be documented.

Exemption certificate management. Collection at the time of sale, validation against the state's requirements, expiration tracking, and periodic refresh. Missing or defective certificates are the most common adjustment in transaction tax audits and the most preventable.

Threshold monitoring. Sales and transaction counts by state, measured against the economic nexus standards adopted after South Dakota v. Wayfair, Inc., with registration triggered promptly on crossing.

Marketplace determinations. Where sales occur through platforms, which party collects for which transactions.

Reconciliation. Tax collected against tax remitted, periodically, since a mismatch is both an exposure and a signal of a system defect.

Instrument 15: the audit response protocol

Purpose. To manage an examination without creating new exposure.

Assign a single point of contact through whom all communications and productions flow.

Log every information request with the date, the scope, the response, and the date produced.

Clear positions before communicating them. An answer given informally by operating personnel becomes the taxpayer's position, and correcting it later is expensive.

Produce the maintained records — the solicitation audit, the unitary file, the sourcing methodology document — rather than reconstructing. A contemporaneous record answers the examiner's question and forecloses the follow-up.

Track the statute. Whether periods are open, whether waivers have been requested, and what the consequences of granting or refusing one are.

Anticipate the three focus areas. Nexus, the unitary determination, and receipts sourcing account for most adjustments in income tax examinations, and taxability and exemption certificates for most in transaction tax examinations.

Preserve procedural rights throughout, since the protest deadline runs from the assessment regardless of ongoing discussions.

A closing note

The instruments here divide into two groups, and the division determines outcomes.

The first group is maintained. The nexus register, the solicitation audit, the unitary file, the sourcing methodology document, the taxability matrix, and the remote employee register are built in the ordinary course and record facts as they occur.

The second group is deployed. The exposure model, the voluntary disclosure analysis, the assessment defense outline, and the audit protocol are used when a question arises.

The second group works only if the first exists. An examination asks why the taxpayer did not file, why income was excluded from the base, and why receipts were sourced as they were — and those are questions about records rather than about doctrine. A business that maintained the first group answers them in an afternoon. A business that did not answers them from recollection, several years after the fact, which is the position from which most assessments become final.

That asymmetry — cheap to build in advance, impossible to build afterward — is the reason a state tax practice organized around maintained records outperforms one organized around argument, however skilled the argument.

It is also the reason the most valuable engagement in this field is frequently the one no client thinks to request: a few days spent building the register, the file, and the methodology document while nothing is pending.

Proposing it, rather than waiting for an assessment to make the case, is the most useful thing counsel in this field can do.

It is rarely urgent and it is almost always the highest-return work available.

Those two facts explain why it is so consistently deferred.

Counsel should say so plainly, and then do the work.

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