Indiana DOR Income Tax Audit Protest

The situation

Robert, 51, owns Precision Stampings Inc., a Muncie, Indiana metal stamping manufacturer with 28 employees producing components for automotive, appliance, and medical device manufacturers across Indiana, Ohio, Illinois, and Tennessee. Annual revenue: $5.2M. In April 2026 he received an Indiana DOR Proposed Assessment: "Indiana Corporate Income Tax: $34,500 (penalty $5,175 + interest $2,800 = $42,475 total), tax period 2022–2024."

The IDOR auditor applied Indiana's throwback rule to $1.1M in Ohio and Illinois sales, attributing them to Indiana's sales factor on the grounds that Precision Stampings is protected by P.L. 86-272 in those states (solicitation-only activities). Robert protests: his Ohio and Illinois activities go beyond solicitation, he has employees who install and test equipment at customer facilities in both states, which creates taxable presence.

Robert has 60 days to file a written protest with IDOR's Legal Division.

(a) The throwback determination depends on a nexus analysis. Indiana's throwback rule only applies if the taxpayer is NOT taxable in the destination state. If Robert's Ohio and Illinois activities create nexus in those states (beyond mere solicitation), Indiana cannot throw back those sales. The test: do Robert's employees in Ohio and Illinois do anything beyond "solicitation" of orders? Installing and testing equipment at customer facilities in Ohio and Illinois almost certainly creates taxable presence, meaning Indiana cannot apply the throwback rule to those sales.

(b) The Letter of Findings stage is the last chance before an independent court. IDOR's Legal Division issues the LOF, it's still an IDOR determination, not independent. If the LOF is unfavorable, the 90-day window to the Indiana Tax Court (independent specialized court) begins. Missing the 90-day Tax Court window means losing the independent review option.

(c) Ice Miller quoted Robert $7,000 for "protest preparation, Legal Division conference, and Tax Court petition if needed." The throwback-rule nexus analysis + written protest + penalty abatement is largely self-executable with the right Indiana-specific framework.

Who receives this

Indiana small and mid-size manufacturers and distributors receiving IDOR income tax assessments for throwback-rule disputes, research expense credit disallowances, or NOL carryforward differences. Primary: Indiana manufacturers with multi-state operations (automotive supply chain, medical devices, industrial equipment) contesting throwback attributions.

Why the agency will not advise you

IDOR cannot advise audit respondents on how to contest its own assessments. INTIME enables electronic protest filing but provides no strategy. ezel.ai has a generic Indiana income tax protest template ($49) but no throwback-rule nexus analysis. Ice Miller, Faegre Drinker, Bose McKinney are the incumbents ($3,000–$12,000). The specific throwback analysis (nexus determination by state) requires Indiana-specific legal reasoning that no generic template provides.

Key facts, with sources

• Indiana's income tax audit protest process: (1) When IDOR issues a Proposed Assessment following an audit, the taxpayer has 60 days to file a written protest to IDOR's Legal Division. The protest should identify each disputed issue, the taxpayer's position, and supporting documentation. IDOR evaluates the protest and issues a Letter of Findings (LOF), which is IDOR's final administrative determination. (2) If the taxpayer disagrees with the LOF, they have 90 days from the LOF date to appeal to the Indiana Tax Court, a specialized court that has exclusive jurisdiction over Indiana tax matters. The Tax Court is independent of IDOR. Electronic filing of protests is available through INTIME (Indiana Taxpayer Information Management Engine); INTIME provides faster processing and allows document uploads. Self-representation is permitted throughout the appeals process, including at the Indiana Tax Court level. Source: DOR Appeals — Indiana Department of Revenue · Indiana Tax Appeals — GetTaxReliefNow · IC 6-8.1-5-1 — Justia Indiana Code 2025
• Indiana uses a single-sales-factor apportionment formula for corporate income tax under IC 6-3-2-2. Indiana has a throwback rule: when a business is not taxable in the state where a sale is delivered (e.g., due to P.L. 86-272 protection for solicitation-only activities), that sale is thrown back to Indiana. This makes Indiana's throwback rule a major audit battleground for multi-state manufacturers and distributors. Indiana's Research Expense Credit (IC 6-3.1-4) provides a credit of 15% of qualified research expenses above a base amount, mirroring federal Sec. 41. IDOR audits frequently dispute: (1) whether activities are 'qualified research' under IC 6-3.1-4's definition (same as Sec. 41 but only Indiana-performed activities qualify); (2) whether certain expenses (contractor research, overhead allocations) properly enter the qualified research expense calculation. Indiana's graduated corporate income tax rate of 4.9% (2024-2025; reduced from prior years under ongoing rate reduction legislation) means smaller assessments than high-rate states, but the throwback rule can create disproportionately large Indiana apportionment for manufacturers. Source: Indiana State Income Tax Protest — ezel.ai (generic template) · An Overview of Indiana Tax Problem Resolution Options — TaxCure

When to bring in a professional

Self-serve responses fit routine cases: clear facts, amounts a business can absorb, and a deadline still ahead of you. Bring in a licensed professional when the amount at stake is large relative to their fee, the facts are genuinely disputed, criminal exposure is possible, or the deadline has already passed. A short paid consultation to sanity-check your plan is often worth it even when you handle the filing yourself.

All sources for this guide

1. DOR Appeals — Indiana Department of Revenue
2. Indiana Tax Appeals — GetTaxReliefNow
3. IC 6-8.1-5-1 — Justia Indiana Code 2025
4. Indiana State Income Tax Protest — ezel.ai (generic template)
5. An Overview of Indiana Tax Problem Resolution Options — TaxCure