IRS Cost Segregation Audit Technique Guide (Pub 5653)

Where this comes from

After the Tax Court's 1997 Hospital Corporation of America decision, taxpayers could once again pull personal property out of a building's cost and depreciate it faster. Cost segregation studies took off. The IRS needed a consistent way for its examiners to review them.

The answer was the Cost Segregation Audit Technique Guide, or ATG. An audit technique guide is a manual the IRS writes to train its own people on one kind of tax issue. The current edition is Publication 5653, stamped with a February 2025 revision date. It collects the law, the court cases, the accepted methods, and the quality standards in one place.

What a quality study looks like, per the guide

Chapter 4 lists the 13 principal elements of a quality study: (1) preparation by a person with expertise and experience, (2) a detailed description of the methodology, (3) use of appropriate documentation, (4) interviews with the right parties, (5) use of a common nomenclature, (6) use of a standard numbering system, (7) an explanation of the legal analysis, (8) determination of unit costs and an engineering take-off, (9) organization of assets into lists or groups, (10) reconciliation of total allocated costs to total actual costs, (11) an explanation of how indirect costs were treated, (12) identification and listing of section 1245 property, and (13) consideration of related issues such as section 263A, accounting method changes, and sampling.

The same chapter lists 9 elements of a quality report: a summary letter, a narrative report, a schedule of assets, a schedule of direct and indirect costs, a schedule of property units and costs, a description of the engineering procedures, a statement of assumptions and limiting conditions, a certification by the preparer, and exhibits.

Chapter 3 walks through six study approaches: detailed engineering from actual cost records, a detailed engineering cost estimate, the survey or letter approach, residual estimation, sampling or modeling, and the rule of thumb approach. The guide makes clear that the level of detail and documentation drives how reliable a study is, and that a bare rule of thumb estimate has little support.

How it shows up in a study

A defensible study is built to the ATG's checklist on purpose. The methodology section, the legal analysis, the cost reconciliation, and the asset-by-asset schedules in our reports map to the 13 study elements and 9 report elements above.

The ATG also matters on exam. The guide says plainly that the degree to which a study conforms to these elements will likely dictate the scope and depth of an examination. A study that hits the quality bar gets a faster, narrower review. A thin one invites a deep dig.

What it does not mean

The ATG is not law. It is not a statute, a regulation, or a ruling, and it does not bind the IRS or a court. You cannot win a dispute just by pointing to it.

Following the guide also does not guarantee the IRS will accept every number in a study. An examiner can still challenge a classification or a cost estimate. The guide sets the quality floor and the review roadmap, nothing more. No study is audit-proof; the goal is a study that holds up when someone checks the work.