Few things produce the kind of stomach-drop feeling that a letter from the IRS does. For most small business owners and individuals, the word "audit" lands somewhere between unsettling and terrifying, even when the return was filed carefully and the numbers are completely accurate. A lot of that anxiety comes from not knowing what actually puts a return on the IRS's radar in the first place.
Understanding what draws scrutiny, and what doesn't, takes a significant amount of guesswork out of the filing process. It also helps business owners and individuals make smarter decisions year-round, not just in April. A CPA can walk any client through the specifics of their own situation, but here's a solid grounding in what the IRS tends to flag and what it generally lets pass.
The IRS Uses Math Before It Uses Judgment
Before any human being at the IRS reviews a return, an automated system called the Discriminant Information Function, commonly called the DIF score, runs a statistical analysis on it. Every return gets scored. The score reflects how far the deductions, income figures, and credits on that return deviate from what the IRS considers statistically normal for someone in that income bracket and filing category.
Returns that score high get flagged for a closer look. Returns that fall within expected ranges typically don't. This is worth understanding because it reframes the audit question. The IRS isn't randomly suspicious. It's running comparisons, and outliers attract attention regardless of whether the numbers are legitimate.
High Deductions Relative to Income Draw Attention
One of the most consistent audit triggers across both individual and business returns is a deduction total that looks disproportionate given the reported income level. Charitable contributions that represent an unusually large percentage of adjusted gross income, business meal deductions that seem high for the industry, and home office deductions that don't hold up to the square footage math all raise the DIF score.
This doesn't mean those deductions shouldn't be taken. Legitimate deductions belong on a return, full stop. What it does mean is that documentation needs to back every single one of them up.
Cash-Heavy Businesses Face Extra Scrutiny
Restaurants, retail operations, salons, contractors, and other businesses where cash transactions are common tend to attract more IRS attention than businesses that run entirely through traceable electronic payments. The IRS knows which industries handle significant cash volume, and it cross-references reported income against what those businesses typically produce.
Reporting income that seems low for the business type, or showing lifestyle indicators that don't match the reported numbers, increases the likelihood of a closer look. Accurate recordkeeping in cash-heavy businesses isn't just good practice. It's the primary defense against an audit turning into something more serious
Round Numbers Signal Estimates, Not Records
A return full of round numbers, $5,000 in supplies, $10,000 in travel, $3,000 in meals, tells the IRS that the figures were estimated rather than pulled from actual records. Real expenses rarely land on perfectly round figures. When a significant portion of a return's deductions are rounded, it’s the kind of signal that nudges a return toward the review pile.
Schedule C Filings Receive Consistent Attention
Sole proprietors filing Schedule C with their personal return have historically faced higher audit rates than other filers. The IRS views Schedule C as a category with elevated risk for underreported income and overstated deductions, partly because there's no separate business entity creating an additional layer of documentation.
Showing a loss on Schedule C is fine when the loss is real and supported. Showing losses year after year on what's supposed to be a business raises the question of whether the activity qualifies as a legitimate business or a hobby, and the tax treatment of those two things differs considerably. A CPA can help establish and document the business purpose clearly enough to withstand that kind of scrutiny.
Not Reporting All Income is a Fast Path to Problems
The IRS receives copies of every W-2 and 1099 issued. When the income reported on a return doesn't match what third parties have already reported to the IRS, the discrepancy gets flagged automatically. This happens more often than people expect, particularly with freelancers juggling multiple clients, investors who receive various 1099 forms, and anyone who changed jobs during the year.
The fix is simple but requires attention. Every income source needs to be accounted for on the return, including smaller amounts that might seem too minor to bother with. If there's any uncertainty about whether something needs to be reported, a CPA is the right person to ask before the return goes in.
What Generally Doesn't Trigger an Audit
Taking legitimate deductions, even large ones, doesn't automatically create audit risk when the documentation supports them. Filing an amended return to correct an honest mistake doesn't flag an account for special attention. Earning a high income by itself isn't a trigger, though it does raise the statistical baseline the IRS uses for comparison. Making a reasonable error on a return that gets corrected through normal correspondence with the IRS is a completely different situation from the kind of patterns that lead to a full examination.
The IRS has limited resources and uses them where the data suggests the highest potential for uncovering problems. Returns that are internally consistent, supported by documentation, and aligned with industry norms for income and expenses tend to move through the system without incident.
An audit isn't a foregone conclusion for anyone who files carefully, keeps solid records, and reports income completely. The vast majority of returns are processed without any additional contact from the IRS at all. For business owners and individuals who want to file with genuine confidence rather than crossed fingers, working with a CPA throughout the year, rather than just at tax time, is the most reliable way to stay on solid ground. Reach out to a CPA to talk through your specific situation and file knowing the return can stand behind every number on it.
by Kate Supino