IRS Audit Process Explained: How the Internal Revenue Service Examines Your U.S. Tax Returns
The Internal Revenue Service (IRS) is the federal authority in the United States tasked with administering and enforcing federal tax laws. Every assessee—whether an individual, partnership, LLC, or large corporation—files income tax returns with the IRS and is accountable to it for the accuracy and completeness of those filings.
An IRS audit often creates additional compliance obligations and can be stressful if one is not prepared. However, with a clear understanding of how IRS audits work, why returns are selected, what information is examined, and how to respond strategically, an assessee can handle the process with confidence.
This article, based on materials published by the IRS and practical experience in handling audits, recasts the core concepts into an easy-to-use guide for assessees who may face an IRS audit now or in the future.
What Is an IRS Audit?
An IRS audit is a formal review of an assessee’s tax return and supporting financial records. The primary purpose is to verify:
- Whether the income, deductions, credits, and other items reported on the return are correctly disclosed under applicable tax law, and
- Whether the correct amount of tax has been computed and paid.
In practice, this means the IRS may ask you to substantiate:
- Income (wages, interest, dividends, capital gains, business income, rental income, etc.)
- Expenses claimed as business deductions
- Itemized deductions (such as mortgage interest, charitable contributions, medical expenses)
- Credits (for example, education credits, dependent-related credits)
The audit is not necessarily an accusation of wrongdoing; many returns are examined simply because they fall within risk parameters or statistical norms created by the IRS.
Types of IRS Audits
The IRS generally conducts three broad categories of audits, depending on the complexity and nature of the issues involved:
1. Correspondence Audit
A correspondence audit is conducted entirely through mail. The IRS sends a notice asking for clarification or documentation relating to specific entries on the return—for example:
- Support for charitable contributions
- Bank or brokerage statements to verify interest or dividend income
- Proof of education expenses or childcare payments
In these cases, the assessee responds by sending copies (or, where permitted, electronic versions) of the requested documents. Many audits end at this stage if the evidence is satisfactory.
2. Office Audit
An office audit is held at an IRS office. The assessee (or representative such as a CPA or enrolled agent) appears in person and brings the requested records. This type of audit is used when:
- The issues are broader than can be efficiently handled by mail, or
- The examiner wants to discuss several points in a single meeting.
The notice of audit will specify:
- Date, time, and location of the meeting
- List of documents and records to be produced
3. Field Audit
A field audit is more extensive and is typically conducted:
- At the assessee’s place of business,
- At the assessee’s home (in some cases), or
- At the office of the assessee’s representative (such as a CPA firm).
Field audits are usually reserved for:
- Businesses and complex individual returns,
- Assessees with multiple sources of income, or
- Cases where significant adjustments may be involved.
How Does a Tax Return Get Selected for Audit?
A. Random Selection and Computer Screening
The IRS uses sophisticated computer systems and statistical models to select returns. Some key elements:
- Statistical formulas: Returns are compared with established “norms” derived from a scientifically valid random sample of returns examined under the IRS National Research Program.
- Deviation from norms: If a return significantly deviates from typical patterns for similar assessees (same income level, profession, type of business, etc.), it may be flagged for further review.
With millions of returns in its database and a long institutional history, the IRS continuously refines its selection criteria based on past audit outcomes.
B. Related Examinations
Returns may also be chosen for audit because they are connected to another return already under examination. For instance:
- Business partners,
- Investors in a partnership or LLC,
- Shareholders in closely held entities involved in related transactions.
If a partner’s return, for example, is under audit and the IRS detects issues affecting the partnership allocations, other partners’ returns may also be selected for examination.