The IRS doesn’t randomly select returns to audit. Its Discriminant Information Function (DIF) scoring system assigns every return a numeric score based on how far it deviates from statistical norms for similar taxpayers. High scores get a second look. Here are the 12 patterns that most reliably raise that score.
1. High income
The simplest trigger: the more you earn, the more likely you are to be audited. In 2023, the IRS audited roughly 0.4% of all individual returns — but 2.4% of returns with income over $1 million. The math makes sense: more revenue potential per audit for the IRS.
2. Unreported income
The IRS receives copies of every W-2, 1099-NEC, 1099-K, 1099-INT, 1099-DIV, and 1099-B issued to you. Its automated matching program cross-references these against your return. If a 1099 you received doesn’t appear on your return, a CP2000 notice — or worse, an audit — is likely incoming. This is the most common audit trigger by volume.
3. Schedule C losses — especially repeated ones
A sole proprietor reporting consistent losses on Schedule C is a significant red flag. The IRS’s hobby loss rules (Section 183) require businesses to show a profit in at least 3 of 5 consecutive years to avoid being reclassified as a hobby — at which point deductions are severely limited. Multiple years of losses, especially combined with high W-2 income, invites scrutiny.
4. Excessive business deductions relative to income
Every industry has statistical norms for expense ratios. A restaurant reporting 95% of revenue as expenses is unusual. A consultant claiming $80,000 in deductions on $90,000 of income triggers DIF scoring. The IRS compares your deductions against what’s typical for your income level and industry.
5. Home office deduction
The home office deduction is legitimate — but historically over-claimed. The IRS knows this. Any home office claim should meet the strict “regular and exclusive use” test, and the calculation should be accurate. The simplified method ($5/sq ft) is less likely to trigger scrutiny than large actual-expense claims.
6. Large or unusual charitable deductions
Charitable deductions are cross-checked against income norms. A taxpayer with $80,000 income claiming $40,000 in charitable deductions is a statistical outlier. Non-cash donations over $500 require Form 8283; over $5,000 require a qualified appraisal. Missing these documents is a quick path to disallowance.
7. Business meal deductions
Meals are 50% deductible — but the IRS knows they’re widely abused. Large meal deductions, meals claimed without adequate documentation, or meal percentages that are high relative to revenue all raise flags. Every meal deduction needs: amount, date, place, business purpose, and who attended.
8. Vehicle deductions — especially 100% business use claims
Claiming 100% business use of a personal vehicle is a significant red flag. Very few people genuinely use a car exclusively for business. The IRS knows this, and without a contemporaneous mileage log, the deduction is extremely vulnerable in an audit.
9. Cash-intensive businesses
Restaurants, bars, hair salons, car washes, and other cash-heavy businesses are perennial audit targets. The IRS has established revenue norms for these industries and flags returns where reported income seems low relative to the type and size of business. Unexplained deposits in bank accounts compared to reported income is a common finding.
10. Rental property losses
Rental activity losses are generally passive losses, deductible against passive income only — unless you’re a real estate professional (750+ hours annually, more than any other profession). Claiming large rental losses as active losses without meeting the real estate professional test is a common audit trigger.
11. Early withdrawal from retirement accounts without penalty
Withdrawing from a 401(k) or IRA before age 59½ normally triggers a 10% penalty. Claiming an exception without the proper documentation — first-home purchase, disability, substantially equal periodic payments — invites verification.
12. Math errors and mismatched information
Simple arithmetic errors, Social Security numbers that don’t match, or income that clearly doesn’t reconcile across forms generate automatic notices. These aren’t audits per se — but they lead to corrections, and patterns of errors can escalate.
Having a red flag ≠ doing something wrong
All of these deductions can be entirely legitimate. The point is to take them with proper documentation, so that if the IRS asks, you can prove every number. A well-documented return with a home office deduction is far safer than an undocumented one — even if the amounts are identical.
What to do if you have red flags
- Document everything contemporaneously — at the time, not later
- Keep receipts, logs, and written records for every significant deduction
- Be accurate — don’t round numbers suspiciously
- If you have complex deductions, consider having a CPA prepare your return
- Don’t omit income — mismatches with third-party reports are almost always caught