The most audit-prone situation for small businesses is consistently reporting large losses on Schedule C, especially across multiple years. The IRS has specific criteria distinguishing legitimate businesses from hobby activities, and repeated losses, particularly when the owner has other substantial income, are a common audit trigger. If your business genuinely loses money, documentation of why and what steps you are taking to become profitable matters.
Unusually high deductions relative to income also draw attention. A home office deduction, vehicle expenses, and meals and entertainment are legitimate deductions, but all three are frequently abused and heavily scrutinized. The IRS compares returns against averages for your industry, if your deduction percentages are significantly above average for a business of your size and type, the return stands out.
A Return Flagged for a Pattern, Not a Single Error
Consider a small consulting business reporting $95,000 in revenue with $61,000 in deducted expenses, a deduction ratio noticeably higher than typical for consulting businesses of similar size, driven largely by a home office deduction claiming 60% of the home's total square footage and a vehicle expense claiming 100% business use with no mileage log to support it. Individually, each deduction might be defensible; together, the pattern is exactly what automated IRS screening tools are built to flag.
When the return is selected for examination, the home office claim cannot be substantiated at anywhere near 60% of the home's actual square footage once the space is properly measured, and the 100% vehicle business-use claim collapses entirely without any log to support it, since the owner also used the same vehicle for all personal errands and family trips. The resulting adjustment reduces the deductions significantly, adds back tax owed, and applies accuracy-related penalties on top. A more conservative, properly documented home office percentage and an honest mileage log from the start would have both survived the audit and likely never triggered the closer look in the first place.
Unreported income is the IRS's primary concern in any audit, and it is easier for them to detect than most business owners assume. The IRS cross-references 1099s filed by your payers against the income you reported. If a client filed a 1099-NEC for $12,000 paid to you and it does not appear on your return, that discrepancy will surface.
Misclassified workers, people doing employee-level work classified as independent contractors, create payroll tax exposure the IRS is specifically looking for. Round numbers on estimated expenses (reporting exactly $10,000 in vehicle expenses, for example) are also statistically unusual and can flag a return as estimated rather than documented.
An S-Corp that pays its owner-employee an unusually low salary is a red flag for the IRS, which regularly identifies distributions that should have been run through payroll. And claiming 100% business use of a vehicle is one of the most commonly disallowed deductions, the IRS expects personal use, and a vehicle used exclusively for business with no personal miles at all is a claim that is rarely accepted without detailed mileage logs.
The most reliable protection against all of these is clean, documented bookkeeping that makes your deductions easy to verify, not just plausible to claim.
The DIF Score, Explained
Many individual and small business returns are scored by an IRS system called the Discriminant Information Function (DIF), which compares your return against statistical norms for similar taxpayers and assigns a score reflecting audit potential. Returns with unusually high scores relative to their peer group get a closer manual review before a decision is made on whether to actually pursue an examination. This is exactly why deduction ratios and expense patterns matter so much, the system is specifically built to flag statistical outliers, not to review every return equally.
Understanding that this is a statistical, comparative process, not a review of your return in isolation, explains why two nearly identical returns can be treated differently if one happens to look like an outlier relative to its specific peer group and the other doesn't.
It's worth having someone review your return specifically with these seven patterns in mind before it's filed, not just checking that the math is correct. A return can be entirely accurate and still carry an unusually high statistical profile in one of these areas, which is worth understanding and being prepared to document, even if nothing was actually done wrong.