Three Types of IRS Audits

The IRS doesn’t run all audits the same way. The type you get depends on the complexity of the issue and the dollar amounts involved. The IRS outlines each type in its audit overview for taxpayers.

Correspondence Audit

This is the most common type. You get a letter — usually a CP2000 notice or a letter asking you to verify a specific item on your return. Maybe the IRS thinks you missed reporting a 1099, or they want documentation for a deduction. You respond by mail with the requested documents, and the IRS either accepts your response or proposes an adjustment. No face-to-face meeting. Most correspondence audits take 3-6 months to resolve.

Office Audit

The IRS asks you to bring records to a local IRS office and sit down with an examiner. These tend to focus on specific issues — itemized deductions, rental income, small business expenses — and they’re more thorough than a correspondence audit. You (or your representative) show up with organized records, and the examiner reviews them on the spot. These are less common than they used to be, partly because the IRS has fewer staff and office space constraints.

Field Audit

A revenue agent comes to your home, business, or your CPA’s office. Field audits are reserved for complex returns — high income, multiple businesses, large deductions, international components. The agent has broader latitude to look at your entire return, not just one issue. These are the most intensive and can take a year or longer. If a revenue agent shows up at your door unannounced, you’re within your rights to ask them to schedule an appointment through your representative.

How the IRS Selects Returns for Audit

There’s no single trigger that guarantees an audit. The IRS uses several methods to flag returns, and sometimes the selection is genuinely random. But some patterns show up more than others.

DIF scoring. Every return gets a Discriminant Information Function (DIF) score, which is a statistical model comparing your deductions and income ratios to similar returns. A high DIF score means your return is an outlier — your deductions are unusually large relative to your income, or your expense patterns don’t match what the IRS expects for someone in your bracket. The exact formula is confidential, but the concept is straightforward: if your numbers don’t look like everyone else’s, you’re more likely to get flagged. The IRS describes the DIF process in the Internal Revenue Manual Section 4.1.3.

Information matching. The IRS receives copies of every W-2, 1099, and K-1 issued to you. Their computers match those documents against your return under the Automated Underreporter (AUR) program. If a 1099-NEC shows you earned $15,000 from a client but you didn’t report it, the system catches that automatically. This is the most common audit trigger, and it’s entirely avoidable — report everything, even if you think the form is wrong (you can dispute the amount separately).

Related returns. If your business partner gets audited, your return might get pulled too. Same if your employer gets audited and your compensation or benefits are part of the issue. The IRS examines related returns to ensure consistency across parties.

Random selection. A small percentage of audits are genuinely random, selected through the National Research Program. These are thorough and cover everything on the return. The goal isn’t to catch fraud — it’s to calibrate the DIF model. Being selected randomly doesn’t mean anything is wrong with your return.

Common Audit Triggers Worth Knowing About

Some return characteristics draw attention more than others. This isn’t an exhaustive list, but these are the ones we see repeatedly in practice:

• High deductions relative to income — Charitable contributions that are 30% or more of AGI, unreimbursed business expenses that seem disproportionate, or large casualty losses
• Schedule C losses year after year — The IRS gets skeptical when a business reports losses for three or more consecutive years, especially if the taxpayer has other income to offset. They’ll look at whether the activity is really a business or a hobby under IRC Section 183
• Earned Income Tax Credit claims — The EITC has one of the highest error rates of any credit, and the IRS audits EITC claims at a higher rate than many other items. The IRS EITC page outlines documentation of qualifying children and income
• Unreported income from crypto or side gigs — The IRS has been ramping up enforcement on cryptocurrency transactions and gig economy income. If you’re on a platform that reported your earnings and you didn’t include them, expect a notice
• Large cash businesses — Restaurants, car washes, laundromats, and other cash-heavy businesses face higher scrutiny because cash income is harder to verify

CP2000 Notice vs. Full Examination

A lot of people confuse a CP2000 notice with a full audit. They’re different.

A CP2000 is an automated notice. The IRS computer found a mismatch between what you reported and what third parties reported. Maybe your broker sent a 1099-B that doesn’t match your Schedule D, or you forgot to report a small 1099-INT. The notice proposes an adjustment and tells you how much additional tax the IRS thinks you owe. You can agree, partially agree, or disagree with documentation.

A full examination (audit) is a human review of your return. An examiner looks at your records, asks questions, and may expand the scope beyond the initial issue. Full exams are less common and more intensive.

The CP2000 is often easier to resolve. If the IRS is right, you agree and pay. If they’re wrong (and this happens — the IRS doesn’t always have the correct basis information on stock sales, for example), you respond with the correct numbers and supporting documents. Most CP2000s get resolved without escalation.

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

The general rule under IRC Section 6501: three years from the date you filed (or the due date, whichever is later). If you filed your 2023 return on April 15, 2024, the IRS has until April 15, 2027 to start an audit for that year.

But there are exceptions that extend the window:

Six years if you underreported gross income by more than 25%. This is called a “substantial understatement” under IRC Section 6501(e), and it gives the IRS double the normal time. The 25% threshold isn’t just about missing a 1099 — it can include overstated basis on asset sales, which effectively understates income.

No limit if you filed a fraudulent return or didn’t file at all. The statute never starts running if there’s no return on file, which is why we always tell people to file even if they can’t pay. Filing starts the clock. Not filing leaves it open forever. For guidance on catching up on unfiled returns, see our guide to filing back taxes.

No limit on certain foreign reporting forms. If you failed to file an FBAR (FinCEN 114) or Form 8938, the statute on those items stays open indefinitely, and the IRS can use them as a springboard to examine other parts of your return.

Your Rights During an Audit

The Taxpayer Bill of Rights gives you specific protections. Most people don’t know about them until they’re already in the middle of an exam:

• Right to representation — You don’t have to face the IRS alone. A CPA, enrolled agent (EA), or attorney can represent you and communicate with the IRS on your behalf. In most cases, you don’t even need to be present. You authorize representation by filing Form 2848 (Power of Attorney)
• Right to know why the IRS is asking for information — The examiner must explain what they’re looking at and why
• Right to appeal — If you disagree with the audit results, you can appeal within the IRS before going to court. The IRS Independent Office of Appeals operates independently from the examination division
• Right to finality — The IRS can’t keep auditing the same item year after year without a good reason. If they examined the same issue in a prior year and made no change, you can raise that as a defense
• Right to a fair and just tax system — If the normal process isn’t working, the Taxpayer Advocate Service (TAS) can intervene on your behalf

Who Should Represent You: CPA, EA, or Attorney?

All three can represent you before the IRS under 31 U.S.C. Section 330 and Treasury Circular 230, but they bring different strengths.

CPAs are the best fit for most audits involving income, deductions, and business returns. They understand the numbers, the forms, and the accounting that underlies the return. If your audit is about whether your deductions are properly documented or your income is correctly reported, a CPA is the right call. That’s what our team does.

Enrolled Agents specialize in tax and are licensed by the IRS itself. They’re strong on individual returns and representation, especially for EITC audits, collections, and installment agreements.

Tax Attorneys are the right choice when the stakes are high — potential fraud penalties, criminal referral risk, or disputes likely to end up in Tax Court. If the issue is legal interpretation rather than accounting, an attorney brings value that a CPA or EA can’t.

For most routine audits, a CPA or EA handles everything. The attorney comes in when the situation escalates beyond a straightforward disagreement about numbers.

The Appeals Process

If the examiner proposes changes you disagree with, you don’t have to accept them. The IRS sends a “30-day letter” giving you 30 days to request an appeal. This is your chance to argue your case before an independent Appeals Officer who wasn’t involved in the original audit. The IRS explains the process in Publication 5, Your Appeal Rights.

Appeals is where a lot of cases settle. The Appeals Office has authority to compromise based on the “hazards of litigation” — meaning they’ll consider the risk that the IRS would lose if the case went to court. This gives you room to negotiate that doesn’t exist at the examination level.

If Appeals doesn’t resolve it, the IRS issues a “90-day letter” (formally, a Notice of Deficiency), and you have 90 days to petition the U.S. Tax Court. Going to Tax Court is a real option for disputed amounts worth fighting over, but it takes time and legal costs. Most taxpayers settle before that point.

How to Respond to an Audit Notice

The first thing to do when you get a notice: read it carefully and note the deadline. Then call your CPA. Don’t call the IRS yourself unless you’re comfortable representing yourself (most people aren’t, and that’s fine). The IRS provides a full guide to understanding notices in Publication 3498, The Examination Process.

Practical steps that make a real difference:

• Respond on time — Deadlines matter. Missing a response deadline can result in the IRS assessing the full proposed amount by default
• Provide only what’s asked for — Don’t volunteer extra information. If the IRS asks for receipts for business travel, send the travel receipts. Don’t send your entire general ledger
• Organize your documents — Number them, label them, and include a cover letter that references the specific items the IRS requested. Examiners appreciate organized responses — it speeds up the process and signals that you take the matter seriously
• Keep copies of everything — Never send originals. Send copies by certified mail or fax (yes, the IRS still uses fax) so you have proof of delivery

Documentation That Holds Up

The best defense in an audit is good records. That sounds obvious, but the standard is more specific than people realize. The IRS wants contemporaneous documentation — records created at or near the time of the expense, not reconstructed later. IRS Publication 463 lays out the documentation requirements for travel, gift, and car expenses in detail.

For business meals, that means a receipt plus a note of who you met with and the business purpose. For vehicle expenses, that means a mileage log (not a year-end estimate). For charitable contributions over $250, that means a written acknowledgment from the charity dated before you filed your return, as required by IRC Section 170(f)(8).

We see clients lose deductions they were entitled to simply because they couldn’t produce the right documentation. The expense was real. The deduction was legitimate. But without the paper trail, the IRS disallows it. Start the habit now, before you ever get audited. For more on organizing your tax documents, see our tax document checklist.

Sources & References

• IRS — Audit Overview for Taxpayers
• IRS — Understanding Your CP2000 Notice
• IRS — Taxpayer Bill of Rights
• IRS Publication 5 — Your Appeal Rights
• IRS Publication 3498 — The Examination Process
• IRS Publication 463 — Travel, Gift, and Car Expenses
• 26 U.S.C. § 6501 — Limitations on Assessment and Collection
• 26 U.S.C. § 183 — Activities Not Engaged In for Profit
• 26 U.S.C. § 170 — Charitable Contributions
• IRS Independent Office of Appeals
• Taxpayer Advocate Service (TAS)
• FinCEN — Report of Foreign Bank and Financial Accounts (FBAR)
• United States Tax Court