The 4 Types of IRS Audits: Identify Yours and Know Your Deadline

If you recently received an IRS audit notice, two things are worth knowing before anything else. Most audits are narrower than they appear on the envelope, and the response window is already running. What you do in the first 30 days will shape the outcome far more than anything you do after. This chapter walks through the four audit types, shows you how to identify yours from the letter code, and explains the steps that matter most in the early days of the process.

The IRS runs four types of audits, and every examination you have heard about is one of these four. The letter code printed on your notice tells you which track you are on, what your deadline is, the likely exposure, and whether this is an audit you can handle yourself or one that needs representation. Our firm has handled thousands of audits across all four types as IRS audit defense counsel. If you would prefer to have a tax attorney review your specific letter and confirm the type, a 15-minute consultation is free.

The Four Types of IRS Audits

Not every audit is the same kind of problem. A correspondence audit is a narrow mail exchange. A field audit is a Revenue Agent arriving at your business with a multi-year scope and a thick stack of document requests. Knowing which track you are on determines everything that follows.

1. Correspondence Audit: The Most Common Examination

A correspondence audit is an IRS examination conducted entirely by mail, limited to one or two specific line items on the return. It is the lowest-severity audit type and the most common, accounting for roughly 75% of all individual examinations the IRS conducts.²

Most correspondence audits are triggered automatically. The IRS’s Automated Underreporter (AUR) system matches every W-2 and 1099 in its database against what taxpayers reported. When the numbers fail to match over a threshold amount, the system generates a CP2000 notice.

An important point for context: a correspondence audit is usually not a person deciding to examine you. It is a computer flagging a mismatch. Common triggers include an unreported 1099, a charitable deduction that is high relative to reported income, a Schedule C with expense ratios outside statistical norms, or an EITC claim the IRS needs to substantiate.

The response deadline is 30 days from the notice date printed on the letter, not 30 days from the day the letter arrives. If the notice sat in the mail for a week, the window is effectively 23 days.

How to Respond to a Correspondence Audit

In our experience, this is where many taxpayers make the audit worse. The instinct is to send the IRS a long explanation with every document available, hoping the issue goes away. That approach almost always creates new issues. The method that works is narrower.

1. Read the notice carefully. Identify the specific tax year, the adjustments proposed, and the documents requested. The scope of the response should match the scope of the question.
2. Gather only the documents that address the request. If the notice asks for substantiation of a charitable deduction, send the charitable receipts. Sending the full Schedule A invites scrutiny of unrelated items.
3. Draft a brief cover letter. One paragraph with taxpayer name, SSN or EIN, notice number, tax year, and a list of what is enclosed. Argument, explanation, and context are not helpful at this stage.
4. Mail copies (never originals) by certified mail, return receipt requested. The IRS occasionally loses mail. The green card is your proof of timely compliance.
5. When penalties are proposed, engage counsel before responding. Accuracy-related penalties under IRC §6662 start at 20% of the understatement and can escalate to 40% or 75% when the examiner identifies fraud indicators.

If the notice involves penalties, a Schedule C business, rental property, or documentation that is less than clear, a brief consultation before responding is worth the time.

2. Office Audit: In-Person, Narrow Scope, Real Stakes

An office audit is an in-person IRS examination held at a local Taxpayer Assistance Center, typically covering three to five specific issues. The examiner is a Tax Compliance Officer (TCO). Average adjustment ranges from $15,000 to $50,000.

The notice arrives as Letter 3572 or Letter 915, directing the taxpayer to appear on a specific date with a specific list of documents. Office audits often appear manageable, and in most cases they are. The complication is that a TCO is trained to ask open-ended questions. Answering one of those without thinking carefully about what else it opens is how office audits grow beyond their original scope. The issues listed in the appointment letter are a floor, not a ceiling.

The issues most frequently examined at the office level:

• Schedule C travel, meals, and entertainment, which are the most-audited deductions in the country
• Rental real estate losses on Schedule E, particularly where passive activity loss rules under IRC §469 may disallow the loss
• Home office deductions, where substantiation under IRC §280A is strict
• Vehicle mileage and depreciation
• Retirement plan contributions

Office Audit Strategy

The examiner is not trying to trap the taxpayer. Their job is to find what is there, and the taxpayer’s job is to answer what was asked. Four rules consistently produce better outcomes.

1. Bring only the documents on the notice. The examiner is entitled to the records listed in the appointment letter, and no more. Bringing additional years or unrelated records is an invitation to widen the audit.
2. Answer narrowly and factually. “Yes,” “no,” “I do not recall,” and “I will need to check my records” are complete answers. The examiner is not owed additional context.
3. When a new issue surfaces, pause the meeting. The taxpayer has the right under IRC §7521(b)(2) to consult a representative before responding to a question outside the original scope.
4. Never sign Form 4549 at the meeting. Form 4549 is the Report of Examination, and signing it waives appeal rights. The taxpayer is entitled to 30 days to review before signing.

3. Field Audit: The Most Serious Civil Examination

A field audit is an IRS examination in which a Revenue Agent visits the taxpayer’s business or home, reviewing the full return across multiple years, often with inventory inspections, employee interviews, and bank deposit analyses. It is the most serious civil examination the IRS conducts and the audit type most likely to result in deficiencies above $100,000.

The notice arrives as Letter 2205-A for individuals or Letter 2205-B for businesses, and the response window is 10 business days to schedule the initial meeting. This is the shortest deadline of any audit type. The examiner is a Revenue Agent, typically a CPA or EA with several years of IRS training.

Our firm regularly handles field audits with proposed deficiencies between $100,000 and several million dollars, particularly on Schedule C businesses above $500,000 in gross receipts, S-corporations and partnerships with complex returns, and high-income individuals with multi-entity structures. The IRS also runs industry-specific sweeps using Audit Technique Guides. Businesses in cash-intensive industries such as restaurants, construction, and auto repair should assume the agent has a playbook before the first meeting.

Field audits should not be handled without representation. This is a practical observation, not a sales position. The initial interview alone can shift the trajectory of the entire examination, and an experienced IRS audit defense attorney manages disclosure to keep scope contained.

The Field Audit Procedure, Step by Step

1. Initial interview. The Revenue Agent visits the place of business and asks about operations, accounting practices, and internal controls. This is the most consequential meeting of the audit. Answers at this stage shape every question that follows.
2. Information Document Requests (IDRs). Written requests covering books, bank statements, general ledger, contracts, invoices, deposit records, and typically the underlying accounting software files.
3. On-site field work. The agent examines records on-site over multiple visits, often spread over weeks or months. Inventory, equipment, premises, and cash-handling procedures may be inspected.
4. Third-party interviews. The agent may interview employees, former employees, vendors, or customers. Under IRC §7602(c), the taxpayer is entitled to advance notice of these contacts.
5. Bank deposit analysis. For cash-intensive businesses, the agent compares total deposits against reported income. Unexplained deposits become presumed income under the Holland v. United States, 348 U.S. 121 (1954) line of cases.
6. Workpapers and proposed adjustments. The agent documents findings, computes proposed adjustments, and drafts Form 4549.
7. Closing conference. A final meeting to review the proposed changes. This is the taxpayer’s opportunity to present defenses before the report is finalized.
8. 30-Day Letter. Formal notice of proposed adjustments with the right to appeal to the IRS Independent Office of Appeals.

Field audits run 12 to 24 months on average, and longer when the entity structure is complex.

4. TCMP / NRP Audit: The Random Research Examination

An NRP audit is a random, line-by-line IRS research examination used to calibrate the agency’s audit selection algorithms. It is not triggered by any suspicion of the taxpayer. The IRS conducts a few thousand of these each year. Selection is entirely random; a taxpayer picked for an NRP audit has not done anything wrong.

The National Research Program (NRP) replaced the older Taxpayer Compliance Measurement Program (TCMP) in 2002. Practitioners commonly describe NRP audits as “deeply unpleasant even when you have done everything right,” which is accurate. The breadth of inquiry reaches areas of the return a targeted audit never would.

NRP Strategy

Because NRP scope is already unlimited, the usual strategy of narrowing issues does not apply. Three priorities consistently produce the best outcomes.

1. Full substantiation across the entire return. Documentation should be pulled for items that would not normally need to be defended in a targeted audit. The examiner will ask.
2. Engage representation immediately. NRP audits run 12 to 18 months and involve extensive records production. A Power of Attorney on Form 2848 means IDRs are sent to the representative rather than the taxpayer.
3. Document rather than argue. The examiner has no deficiency target. The goal is clean records. Theoretical argument invites scope expansion.

Most NRP cases close with minor adjustments or no change at all. When they do produce a deficiency, the case can be appealed through the same process as any other examination.

How Far Back Can the IRS Go? The Statute of Limitations

This is typically the first question any audited taxpayer asks. The answer depends on which audit type is involved and what the examiner finds. Under IRC §6501, three rules govern how far back the IRS can reach.

• 3 years (standard rule). The IRS has 3 years from the filing date or the due date, whichever is later, to assess additional tax. This is the default for most correspondence and office audits.
• 6 years (substantial omission). When more than 25% of gross income has been omitted, the statute extends to 6 years. This is the rule field auditors commonly invoke when the bank deposit analysis identifies unreported income.
• No statute (fraud or unfiled returns). When fraud can be proven, or when a return was never filed, there is no statute of limitations. The IRS can assess tax for any year, indefinitely. This is why fraud penalty referrals are significant: they open every year.
• FBAR and foreign asset penalties. 6 years for non-willful violations, no statute for willful. These run parallel to income tax statutes.

Note for fraud or unfiled-return cases: when the statute is open indefinitely, immediate counsel and (in some cases) voluntary disclosure are critical to limit exposure. A confidential consultation can be arranged the same day.

Field audits frequently open on a single year and expand backward as the examiner identifies patterns. At some point, the agent may ask the taxpayer to sign Form 872, a waiver that voluntarily extends the statute. Form 872 should never be signed without counsel reviewing whether the extension actually benefits the taxpayer or only benefits the government.

Actual Audit Selection Rates by Income and Return Type

Overall audit rates for individual returns have declined to approximately 0.4% in recent years, according to the IRS Data Book. The headline number is reassuring but it conceals substantial variation. Audit odds are meaningfully different depending on income and return type.

These rates are trending upward. The Inflation Reduction Act funding directed new enforcement resources specifically at filers above $400,000. The top brackets should expect higher audit rates in the coming filing years, not lower.

The Audit Escalation Pathway

Audits do not always stay where they start. The escalation pathway from correspondence to office to field to criminal investigation is real, and understanding what triggers each jump is the difference between a managed examination and a cascading loss.

Correspondence to Office or Field

A correspondence examiner refers the case to in-person examination when any of the following occurs: (a) the taxpayer’s response reveals issues beyond the original question, (b) the documents submitted show discrepancies pointing to broader underreporting, (c) the examiner identifies what the IRS describes as “indicia of fraud,” such as duplicate books, altered documents, or unexplained cash, or (d) new third-party information returns appear after the response is filed. This is the primary reason we consistently advise taxpayers to answer the question that was asked, and nothing else.

Office to Field

Office audits escalate to field examination when the Tax Compliance Officer reaches the limits of their authority. Business returns with meaningful complexity, multi-entity structures, or any matter requiring on-site inspection typically moves up. Once a case has been referred to field, it stays at field.

Field to Criminal Investigation

A Revenue Agent is required to refer a case to IRS Criminal Investigation when firm indications of fraud are present. The standard is set out in Internal Revenue Manual Part 25.1.2, and includes consistent patterns of unreported income, false statements during the audit, concealment of assets, and obstructive behavior. Once a case has been accepted for criminal investigation, the civil audit pauses. A criminal tax case cannot be settled with a payment.

The practical implication is this: what a taxpayer says and produces during a correspondence or office audit directly controls whether the examination escalates. We regularly see cases that started as a $5,000 mismatch grow into $150,000 field audits because the initial response opened additional issues. An IRS audit defense attorney manages that disclosure to keep the audit contained to its original scope.

The First 48 Hours After Receiving an Audit Notice

The actions taken in the first two days after an audit notice arrives shape the outcome disproportionately. The following sequence reflects what we consistently recommend to new clients.

1. Do not call the IRS yet. The telephone number printed on the notice connects to an examiner who opens a contact record the moment the call is answered. Statements made during that call become part of the examination file. Counsel should be engaged first.
2. Photograph the envelope. The postmark starts the response clock, not the date the envelope was opened.
3. Identify the letter code. The letter identification table above confirms the audit type and the deadline.
4. Verify the notice is legitimate. Scam audit notices exist. Genuine IRS notices include an IRS address, a notice number in the upper right, and never threaten immediate arrest or demand payment by gift card or wire transfer.
5. Do not pull documents yet. Gathering records before the scope is clear risks producing more than is required. Counsel identifies the minimum sufficient response.
6. Do not amend the return. Filing Form 1040-X during an open audit is almost always the wrong move and can be treated as admission evidence.
7. Engage a tax attorney for an intake call. The intake confirms the audit type and deadline, and a Form 2848 Power of Attorney places the attorney between the taxpayer and the examiner. Further contact from the IRS goes to the attorney, not to the taxpayer.

When to Engage an IRS Audit Defense Attorney

Not every audit requires counsel. A CP2000 for a missing 1099 that can be documented in 20 minutes generally does not warrant professional representation. The situations below are the ones where the cost of self-representation almost always exceeds the fee for counsel.

• Field audit notice (Letter 2205-A or 2205-B). Field audits should not be handled without representation. The initial interview alone can shift the trajectory of the entire examination.
• Proposed deficiency above $10,000. See the ROI note above.
• Business returns (Schedule C, S-corporation, partnership) or multi-entity individual returns. Business audits expand quickly. Counsel narrows them.
• Fraud penalties on the table. Form 886-A language citing IRC §6663 (civil fraud, 75%) or accuracy-related penalties under §6662 is a signal to engage counsel immediately. These are pre-criminal indicators.
• The examiner is asking about bank deposits exceeding reported income. This is the single most common fraud lead. Questions should stop until counsel is engaged.
• The case is being referred to Criminal Investigation. At that point, representation should come from a criminal tax defense attorney, not a CPA.
• The audit is expanding mid-examination. A correspondence audit that has grown into office or field is signaling danger. Representation should be secured before the next meeting.

Frequently Asked Questions

Next Steps in This Guide

The appropriate next chapter depends on your situation.

• To understand how the IRS selects returns for audit: Why the IRS Audits Tax Returns.
• To prepare a response: IRS Audit Strategy.
• To reduce the risk of future audits: IRS Audit Red Flags & Risk Reduction.
• If the audit has concluded and the result is in dispute: Appealing an IRS Audit.
• If the audit closed without a timely response: Audit Reconsideration.
• To engage representation: IRS Audit Defense Attorney.

If you would prefer to have someone walk through your specific notice with you, a 15-minute consultation is free. We will tell you what you are facing and what the path forward looks like, whether that involves our firm or not.