An IRS audit is usually triggered when a return’s numbers don’t line up with the income data the IRS already has, or when deductions, credits, or business losses fall outside the statistical norms for a given income level. Selection is almost never random. Two automated systems score every return filed, and the ones that deviate most from expected patterns get pulled for human review. Knowing what triggers an IRS audit comes down to knowing what those systems are looking for.
How the IRS Decides Which Returns to Examine
Every return runs through at least two layers of screening. The first is an income-matching program that compares what you reported against the W-2s, 1099s, and other information returns the IRS receives from employers, banks, and brokerages. The second is the Discriminant Function System, or DIF, a statistical tool that rates each return on how likely an examination is to produce additional tax. A companion score, the Unreported Income DIF, rates the likelihood that income was left off entirely. Returns with high scores get flagged, and an IRS employee then decides whether to open a full examination.1IRS. The Examination (Audit) Process – Section: Computer Scoring
The practical takeaway: the IRS isn’t guessing. It’s working from historical patterns of what accurate returns look like at each income level, and the returns that stand out are the ones that get attention.
Income That Doesn’t Match Third-Party Reports
The single most common trigger is a mismatch between what you report and what payers told the IRS you earned. Employers file W-2s. Banks and brokerages file 1099s for interest, dividends, freelance payments, retirement distributions, and more.2Internal Revenue Service. About Form W-2, Wage and Tax Statement When the totals on your return don’t match the totals in the IRS’s file, the automated system catches it, often within months of filing.
The result is typically a CP2000 notice. It isn’t technically an audit, but it functions like one: the IRS proposes changes to your return and calculates the extra tax owed based on the income you left off.3Internal Revenue Service. Understanding Your CP2000 Series Notice Forgetting a small 1099-INT from a savings account or overlooking a one-off freelance payment is enough to generate one. If the underpayment goes unresolved and the IRS finds negligence or disregard of the rules, it can assess an accuracy-related penalty of 20% of the underpayment.4Office of the Law Revision Counsel. 26 USC 6662 – Imposition of Accuracy-Related Penalty on Underpayments
Before filing, gather every W-2 and 1099 you received and confirm the totals match what you’re about to report. If a form arrives late, wait to file or amend afterward.
Deductions That Look Too Large for Your Income
The IRS maintains statistical averages for deductions at every income level. When your charitable giving, medical expenses, or other write-offs land far above that average, your DIF score reflects it.
Charitable contributions draw particular attention. Someone reporting $50,000 in adjusted gross income who claims $20,000 in donations is a clear outlier. For any single gift of $250 or more, the IRS requires a written acknowledgment from the recipient organization, and you must have it in hand before filing rather than scrambling for it after a notice arrives.5Internal Revenue Service. Publication 526 (2025), Charitable Contributions – Section: Contributions of $250 or More Non-cash donations above $5,000 generally require a qualified appraisal attached to the return.
Large deductions aren’t off-limits. But if you claim them, you need receipts, statements, canceled checks, and acknowledgments capable of surviving a document request.
Self-Employment and Small Business Red Flags
Schedule C filers face higher audit risk than W-2 employees because self-reported income and expenses are easier to manipulate than payroll figures. A few patterns draw the most scrutiny.
Repeated Losses and the Hobby Loss Rule
Reporting net losses from a side business year after year is a magnet for review. Under Internal Revenue Code Section 183, an activity is presumed to be for-profit if it turns a profit in at least three of the last five tax years. Fail that test, and the IRS can reclassify it as a hobby.6Office of the Law Revision Counsel. 26 USC 183 – Activities Not Engaged in for Profit Reclassification eliminates your ability to deduct the activity’s expenses against other income, which can produce a substantial bill.
Examiners look at whether you run the activity in a businesslike manner, keep separate books, put real time into it, and depend on the income. A photography side venture claiming $15,000 in gear and travel against $2,000 in revenue, with no visible marketing or clients, is exactly the profile they target.
Home Office and Vehicle Deductions
The home office deduction requires that the space be used regularly and exclusively for business.7Internal Revenue Service. Topic No. 509, Business Use of Home A corner of the dining table that doubles as homework space doesn’t qualify. You need records showing which part of your home qualifies, how it’s used, and the associated expenses.8Internal Revenue Service. Publication 587 (2025), Business Use of Your Home – Section: Recordkeeping
Vehicle deductions trip up more self-employed taxpayers than any other category. Claiming 100% business use of a car you also drive to the grocery store is a red flag examiners see constantly, and it rarely survives review. The IRS expects a contemporaneous mileage log with dates, destinations, business purpose, and miles driven. Without one, the entire deduction is at risk, not just the personal-use portion.
Worker Classification
Businesses that pay the same worker on both a W-2 and a 1099, or that issue 1099s to people who function like employees, invite examination. The IRS specifically instructs examiners to compare W-2 and 1099 filings for the same workers as a screening step.9Internal Revenue Service. Form W-2 and Form 1099-MISC Filed for the Same Year Misclassifying employees as independent contractors avoids payroll taxes, and the IRS treats that revenue loss seriously. If your business relies heavily on 1099 labor, be prepared to show the classification holds up under the IRS’s common-law test for worker status.
Cash, Foreign Accounts, and Crypto
Certain transactions carry their own reporting rules. Missing them creates independent triggers, and the penalties are steep.
Large Cash Transactions
Any trade or business receiving more than $10,000 in cash from a single transaction, or from a series of related transactions, must report it on Form 8300.10Internal Revenue Service. Form 8300 and Reporting Cash Payments of Over $10,000 Banks file a separate Currency Transaction Report. The IRS cross-references these with tax returns to spot unreported income. A pattern of deposits kept just under $10,000, known as structuring, is itself a federal crime even if the underlying money is legitimate.
Foreign Financial Accounts
If your foreign bank and financial accounts exceed $10,000 in combined value at any point during the year, you must file FinCEN Form 114 (the FBAR).11Financial Crimes Enforcement Network. Report Foreign Bank and Financial Accounts Separately, the Foreign Account Tax Compliance Act requires you to report specified foreign financial assets on Form 8938 if their combined value exceeds $50,000 at year-end for single filers living in the U.S. (thresholds are higher for joint filers and taxpayers abroad).12Internal Revenue Service. Summary of FATCA Reporting for U.S. Taxpayers
The penalties are harsh. Civil penalties for a non-willful FBAR violation can reach $10,000 per account per year, and willful violations carry penalties up to $100,000 or 50% of the account balance, whichever is greater, plus potential criminal prosecution. Skipping a required Form 8938 also prevents the statute of limitations from starting on your entire return, meaning that year stays open indefinitely.
Cryptocurrency and Digital Assets
For transactions on or after January 1, 2025, cryptocurrency exchanges and other digital asset brokers must report sales proceeds to the IRS on Form 1099-DA. Cost basis reporting on certain transactions begins January 1, 2026.13Internal Revenue Service. Final Regulations and Related IRS Guidance for Reporting by Brokers on Sales and Exchanges of Digital Assets The same income-matching system that catches missing W-2s now applies to crypto. Unreported gains from digital asset sales will increasingly generate automated mismatch notices.
Refundable Credits, Especially the EITC
Refundable credits pay out even when you owe no tax, so the fraud risk runs toward the government and the IRS scrutinizes them harder. The Earned Income Tax Credit is the clearest example. EITC claimants have historically faced audit rates comparable to taxpayers earning over $1 million, despite their far lower incomes, because the eligibility rules around qualifying children and filing status are frequently applied incorrectly. If you claim the EITC, keep documentation of the child’s residency, your relationship to the child, and your earned income: school records, medical records, pay stubs.
Education credits like the American Opportunity Credit also draw automated checks. The IRS matches your claim against Form 1098-T data from the school, and any discrepancy triggers correspondence.
High Income
Income level by itself is a selection factor. IRS data shows audit rates of roughly 0.1% to 0.2% for taxpayers earning between $25,000 and $500,000, about 1.3% for those earning between $1 million and $5 million, and 8.7% above $10 million based on the most recent completed examination cycles.14IRS. IRS Statement – Updated IRS Audit Numbers The agency concentrates experienced field agents on high-income individuals because each examination recovers more revenue.
Complexity is part of it. High earners are more likely to hold partnership interests, rental portfolios, foreign investments, and pass-through entities, each adding layers the IRS wants to verify. Under the Bipartisan Budget Act’s centralized partnership audit regime, the IRS can now assess underpayments at the partnership level rather than chasing individual partners, making these structures more efficient to examine.15Internal Revenue Service. BBA Centralized Partnership Audit Regime
Math Errors and Suspiciously Round Numbers
Arithmetic errors get caught instantly by IRS computers. Adding Schedule C expenses wrong, miscalculating a credit, transposing digits: these usually generate a correction notice rather than a full audit. But repeated errors, or errors that always happen to favor the taxpayer, escalate scrutiny.
Round numbers are subtler. Reporting exactly $5,000 for office supplies and $2,000 for travel signals estimation, not receipts. Real expenses rarely land on tidy figures, and examiners know it. A return full of round numbers invites a closer look at whether the expenses happened at all.
How to Reduce Your Audit Risk
Most triggers come down to two things: reporting all your income, and being able to prove every deduction you claim.
- Match your reported income to every W-2 and 1099 you received before filing.
- Keep receipts, acknowledgments, and appraisals for large deductions, especially charitable gifts of $250 or more.
- Maintain a contemporaneous mileage log for any vehicle deduction, and confirm your home office is used regularly and exclusively for business.
- File Form 8300, the FBAR, and Form 8938 when the thresholds apply. The penalties for missing them are worse than the tax at stake.
- If a side business shows losses year after year, be ready to show it’s run in a businesslike way, or expect the hobby loss rule to come up.
- Report digital asset sales. Broker reporting is now in effect, and mismatches will surface automatically.
None of this makes an audit impossible. High-income returns and complex returns get looked at regardless. But the returns that get pulled from the middle of the income distribution almost always share the same features: a number that doesn’t match, a deduction that doesn’t fit, or a form that should have been filed and wasn’t.