What Are Common Reasons the IRS Selects a Return for Audit?
Very few returns get audited in any given year, and the ones that do usually get flagged through a mix of methods rather than one obvious trigger.
The short answer
Returns are generally selected for audit through a combination of automated statistical scoring that compares a return against typical patterns for similar filers, information mismatches with data reported by employers or other payers, links to another audited return, such as a business partner or investor, and a smaller share of purely random selection. No single item on a return guarantees an audit, and most returns are never examined at all.
Statistical scoring
The IRS uses scoring formulas that compare a return’s figures against statistical norms for similar income levels and filing types. A return with unusual ratios — for example, deductions that are large relative to reported income — can score higher and get flagged for a closer look, though a high score alone doesn’t mean an audit will follow.
Information mismatches
When income or other figures on a return don’t match what employers, banks, or other payers reported separately to the IRS, that discrepancy can prompt further review. This is the same underlying mismatch that often generates an automated notice, like a CP2000, rather than a full audit — but a bigger or repeated mismatch can sometimes lead to deeper examination.
Self-employment income and related examinations
Income that isn’t automatically reported by a third party, such as earnings reported on a Schedule C for self-employed work, tends to draw somewhat more scrutiny simply because there’s no matching document for the IRS to cross-check it against. That doesn’t mean self-employment income is inherently risky to report — it just means there’s more manual verification involved on both sides. A return can also get pulled into review because it’s connected to another filer or entity already under examination, such as a business partner or a shared investment, which isn’t a judgment on the individual return so much as a byproduct of reviewing a connected filing.
Random selection
A portion of audits are chosen through pure random sampling, independent of anything specific about the return, as part of a research program the IRS uses to measure overall compliance patterns. A random selection isn’t a reflection of anything unusual about the filer.
What to weigh
None of these categories function as a guarantee, and being flagged for one doesn’t necessarily mean a problem will be found — an audit can end with no change at all. Keeping organized records that support what’s reported, regardless of which category might apply, is the practical constant across all of them. Understanding how far back a return can typically be audited is also useful context, since it shapes how long those supporting records are generally worth keeping.
A practical habit
Because audit selection blends automated scoring, mismatches, and random chance, there isn’t a simple checklist that guarantees avoidance. Filing accurately, keeping supporting documentation, and responding promptly if a notice or audit letter does arrive are the factors within a filer’s control.