Records, Substantiation, and the Cohan Line
Deductions are a matter of legislative grace — the burden of proving them sits on the taxpayer. That is the hard rule. The merciful one is the Cohan doctrine: where records are imperfect but the expense clearly happened, estimation is sometimes allowed. Between those two poles sits the statute that catches most people: Section 274's heightened substantiation rules for travel, meals, autos, and gifts, where estimation is forbidden entirely and "close enough" is disallowed in full. Knowing which rule governs which expense is the whole game when the IRS asks for proof.
What this stage covers
This chapter addresses the substantiation requirements for ordinary business expenses—the most common source of disputes between taxpayers and the IRS. It traces the doctrine from the Cohan rule, which allowed courts to estimate deductible expenses when exact records were unavailable, through Congress's response imposing strict substantiation requirements under Section 274(d) for travel, meals, entertainment, gifts, and listed property. The chapter explains how these strict rules eliminate judicial estimation for covered categories, meaning taxpayers who fail to maintain adequate records lose the deduction entirely.
The chapter then examines the current and emerging enforcement landscape, including the Automated Underreporter program, the Automated Collection System, and the growing use of artificial intelligence to identify suspicious deduction patterns at scale. It argues that substantiation is not merely a compliance burden but a strategic asset, and it demonstrates how contemporaneous recordkeeping integrated into the Examination File methodology transforms a vulnerable taxpayer position into a defensible one. The chapter concludes that the future of expense enforcement is automated notices with minimal human involvement, making systematic recordkeeping architecture essential for practitioners and their clients.
The map — how the book walks it (Chapter 20)
- 20.1 The Cohan Rule: Foundation and Limits — The judicial estimation doctrine from Cohan v. Commissioner and how Section 274(d) eliminated it for travel, meals, entertainment, gifts, and listed property.
- 20.2 The Automated Enforcement Terrain — How AUR computer matching, ACS collection automation, and AI-enhanced case selection are replacing labor-intensive examinations with scalable notice-based enforcement.
- 20.3 Substantiation as Strategic Defense — Why contemporaneous records are a strategic asset: they enable fast, thorough responses to notices that close cases, while missing or reconstructed records leave taxpayers defenseless.
- 20.4 Integration with Planning and Compliance Architecture — How substantiation fits into the Monthly Trident Cadence and shapes expense planning decisions such as mileage reimbursement versus company car and actual meals versus per diem.
- 20.5 The Future Is More Letters, Fewer People — The enforcement shift toward automated notices and reduced human review, making systematic recordkeeping the defining difference between practices that resolve matters quickly and those that face protracted disputes.
Who needs this
Tax practitioners and advisors serving small business owners, rental property owners, and self-employed individuals who claim deductible expenses on Schedules C, E, or F and face increasing automated scrutiny of those deductions.
What representation changes
A representative's job in a records case is triage: which items are strictly substantiated, which can be reconstructed, which qualify for estimation, and which to concede so the rest survive. That allocation decides the outcome more than any single receipt.