What the IRS Actually Checks in an Audit — and the Three Things They Almost Always Want

Quick note: This post explains how IRS audits work, the three types of examination you might face, and the specific documents examiners request most often. It is educational only and does not constitute legal or tax advice. If you receive an audit notice or suspect criminal exposure, consult an enrolled agent, CPA, or tax attorney before responding.

The three types of IRS audits—and which one you're most likely to see

The IRS conducts examinations in three formats, each with different stakes and procedural rules. A correspondence audit is handled entirely by mail. The IRS sends a notice—often a CP2000 or Letter 525—questioning one or two line items on your return. You respond by mailing documentation, and the examiner closes the case or issues an adjustment. Correspondence audits account for roughly three-quarters of all individual examinations and typically resolve within 90 to 180 days.

An office audit requires you to appear at a local IRS office with your records. The examiner schedules an appointment, reviews documents in person, and may ask follow-up questions. Office audits are less common than correspondence exams but more intensive; they often involve multiple Schedule C deductions, itemized-deduction bunching, or dependent-verification issues.

A field audit is the most comprehensive. A revenue agent visits your home, business, or representative's office to inspect books, records, and sometimes physical assets. Field audits are reserved for high-income returns, complex business structures, or cases flagged by the IRS Criminal Investigation division. They can span twelve months or longer and may expand beyond the original scope if the agent discovers additional issues under IRM 4.10.3. If you receive a field-audit notice, retain professional representation before the first meeting.

What triggers an audit in the first place

IRS audit selection is driven by the Discriminant Information Function (DIF) score, third-party information-return matching, and manual review by revenue agents. The agency does not publish DIF thresholds, but decades of practitioner experience reveal consistent patterns. Unreported income is the single largest trigger. Every Form W-2, 1099-NEC, 1099-K, and 1099-INT the IRS receives is matched to your return by Social Security number. If a payer reports $8,000 in freelance income and you omit it, the IRS computer flags the discrepancy and generates a CP2000 notice.

Large or unusual deductions relative to your income bracket invite scrutiny. A $40,000 charitable contribution on $80,000 of adjusted gross income is statistically anomalous and will elevate your DIF score. Similarly, a sudden spike in business expenses—travel jumping from $3,000 to $18,000 year-over-year with no corresponding revenue increase—draws attention.

Schedule C net losses, especially repeated losses over multiple years, signal potential hobby-loss reclassification under IRC § 183. If your side business shows a loss in eight of the last ten years and you claim those losses against W-2 income, the IRS may argue the activity lacks a profit motive and disallow the deductions.

Head of Household filing status is another frequent audit target. To qualify, you must be unmarried, pay more than half the cost of maintaining a home, and have a qualifying dependent living with you for more than half the year. The IRS sees inflated refunds when taxpayers incorrectly claim HoH, so examiners routinely request school records, lease agreements, and utility bills to verify the dependent's residence.

The three things the IRS almost always wants

Regardless of audit type, examiners consistently request the same core documentation. First, proof of income. Bring copies of all Forms W-2, 1099-NEC, 1099-MISC, 1099-K, 1099-INT, 1099-DIV, and any other information returns you received. If you operate a cash business, provide bank statements, point-of-sale reports, and deposit records that reconcile to the gross receipts reported on Schedule C. The IRS will perform a bank-deposit analysis if your records are incomplete, and unexplained deposits are presumed to be taxable income unless you prove otherwise.

Second, substantiation for every deduction or credit in dispute. Under IRC § 6001 and Treasury Regulation § 1.6001-1, you must keep records sufficient to establish the amount, time, place, and business purpose of each expense. For travel and meals, that means receipts, itineraries, and a contemporaneous log noting the business reason. For charitable contributions over $250, you need a written acknowledgment from the charity that states the amount and whether you received goods or services in return. For vehicle expenses, IRS Publication 463 requires a mileage log with date, destination, miles driven, and business purpose for each trip. A reconstructed log prepared after the audit notice arrives is weaker evidence, but courts have accepted reasonable approximations when corroborated by appointment calendars or client invoices.

Third, contracts, invoices, and agreements that demonstrate the legitimacy of transactions. If you deducted $15,000 in consulting fees paid to a related party, the examiner will ask for a written contract, invoices detailing services rendered, proof of payment, and evidence that the recipient reported the income. If you claimed a home-office deduction, provide a floor plan, photographs, utility bills, and a lease or mortgage statement. The IRS is not looking for perfection—it is looking for credible, contemporaneous records that prove the expense occurred and served a deductible purpose.

What happens during a correspondence audit

A correspondence audit begins with a letter identifying the tax year and line items under review. The notice includes a response deadline—typically 30 days—and instructions for submitting documentation. You may mail copies of receipts, statements, and explanations directly to the address on the notice, or you can upload them through the IRS Document Upload Tool if the letter includes an access code.

The examiner reviews your submission and issues one of three outcomes: full allowance of the deduction (no change), partial allowance (some expenses disallowed), or full disallowance with a proposed tax, penalty, and interest assessment. You have the right to appeal any adverse determination to the IRS Independent Office of Appeals under IRM 8.6.1 before the assessment becomes final. If you agree with the adjustment, you sign the response form and pay the balance or request an installment agreement.

Correspondence audits are narrow in scope. The examiner cannot expand the audit to other years or other line items without issuing a new notice and following separate procedures. That limited scope is both a safeguard and a reason to respond promptly—silence often results in a default assessment based on the IRS's proposed adjustment.

What happens during an office or field audit

Office and field audits involve face-to-face interviews. The revenue agent or tax compliance officer will ask about your occupation, sources of income, business operations, and financial habits. They may request a tour of your business premises, examine inventory or equipment, or interview employees. Under IRM 4.10.4, the agent can expand the scope of the audit if they discover issues that suggest fraud, substantial underreporting, or related-party transactions.

You have the right to representation at every stage. An enrolled agent, CPA, or attorney can attend meetings on your behalf, answer questions, and negotiate with the examiner. In many field audits, taxpayers never speak directly to the agent; the representative handles all communication. This is especially important if the agent begins asking about intent, prior-year patterns, or the source of large deposits—questions that can signal a referral to IRS Criminal Investigation.

At the conclusion of the audit, the agent issues a Revenue Agent Report (RAR) detailing findings, adjustments, and the legal basis for each change. You have 30 days to agree, appeal to the Office of Appeals, or petition the U.S. Tax Court if a statutory notice of deficiency is issued. Most cases settle at the Appeals level; fewer than 10% proceed to Tax Court litigation.

Red flags that mean you need professional help immediately

Certain audit scenarios carry criminal exposure and require immediate representation. If the revenue agent asks whether you intended to omit income, whether you keep a second set of books, or whether anyone helped you prepare the return, stop answering questions and consult a tax attorney. Those questions appear in the IRS fraud-development checklist under IRM 25.1.2. Similarly, if the agent mentions a "special agent" or says the case has been referred to Criminal Investigation, do not provide any further statements without counsel present.

Any field audit—regardless of issues—warrants professional representation. The stakes are higher, the agent has broader authority, and missteps can result in multi-year adjustments or penalties. If your audit involves offshore accounts, cryptocurrency transactions, payroll-tax trust-fund issues, or allegations of filing false returns, retain an attorney who can invoke attorney-client privilege and coordinate with the IRS on your behalf.

How Tax Advocate Group helps clients prepare for and respond to IRS audits

When you receive an audit notice, time matters. Tax Advocate Group reviews the notice, identifies the issues in dispute, and builds a documentation package that directly addresses the examiner's concerns. We gather receipts, reconcile bank statements, reconstruct missing logs, and prepare written explanations that comply with IRS substantiation rules. If records are incomplete, we work with you to develop secondary evidence—calendars, emails, photos, third-party affidavits—that courts and examiners accept when primary documentation is unavailable.

We represent you at every interaction. For correspondence audits, we submit responses on your behalf and negotiate partial allowances when appropriate. For office and field audits, we attend all meetings, manage the flow of information, and ensure the agent does not expand the scope without proper authority. If the case escalates to Appeals or Tax Court, we coordinate with counsel and provide continuity from the first notice through final resolution.

Our goal is not to eliminate every adjustment—it is to ensure you pay only what the law requires, with penalties and interest minimized through accurate documentation and procedural compliance. Audits are not automatic losses. With preparation and representation, many examinations close with no change or minor adjustments that taxpayers can afford.

Bottom line: Most IRS audits are correspondence exams that focus on one or two line items, and they hinge entirely on your ability to produce credible, contemporaneous documentation. Unreported income, large deductions, Schedule C losses, and Head of Household claims are the most common triggers, and examiners almost always request proof of income, receipts for disputed expenses, and contracts or logs that establish business purpose. If you face a field audit or suspect criminal exposure, retain professional representation before responding. Tax Advocate Group helps taxpayers prepare documentation, respond to examiner requests, and navigate Appeals when necessary—ensuring you pay what you owe, not what the IRS assumes.