For all the anxiety the word generates, an audit is a rare event. IRS Data Book statistics show the agency has examined well under one percent of individual income tax returns in recent years, on the order of a few returns out of every thousand filed, with the odds rising mainly at very high incomes. The agency’s own published data makes the picture plain: most filers will go decades without ever being examined.
So who does get picked, and why? The selection process is less mysterious than folklore suggests. The IRS describes its methods openly, and understanding them does two useful things: it tells you which habits actually raise your odds, and it helps you recognize the difference between a real examination and the far more common computer-generated mismatch notice.
How the IRS picks returns
The IRS explains on its audits page that returns reach the examination pile a few main ways. The biggest is computer screening. Every return receives a score from the Discriminant Function system, or DIF, a statistical formula that compares your deductions, credits, and income mix against norms for returns like yours. The higher the score, the more your return stands out from its peers, and high scorers get a human review to decide whether an exam is worth opening.
A second route is the related examination. If your business partner, employer, or an investor in the same deal is under audit, transactions that flow through to your return can pull it in too. Finally, a small number of returns are chosen essentially at random under research programs the IRS uses to measure overall compliance and to recalibrate those DIF formulas. Random selection means a perfectly clean return can be examined; it is nobody’s fault and no accusation.
The mismatch notice that is not an audit
Far more common than any audit is document matching. Employers, banks, brokers, and gig platforms send the IRS copies of your W-2s and 1099s, and computers compare those totals to what your return reports. When the numbers disagree, the system generates a CP2000 notice proposing a change to your tax. The IRS itself notes that a CP2000 is not an audit; it is an automated proposal you can agree with or contest with documentation.
The practical lesson is that unreported income is the most mechanical trouble you can buy. A forgotten 1099 from a side gig or a brokerage account will surface on its own, no auditor required. Report everything that generates a form, even when no tax ends up due.
What raises a DIF score
The exact formula is confidential, but its logic is not: it flags returns that look unusual next to statistically similar ones. Deductions far out of proportion to income, a business that reports losses year after year while the household somehow pays its bills, heavy vehicle or travel write-offs, and large round numbers that suggest estimates rather than records all push a return away from its peer group. Cash-heavy businesses draw attention because there is no third-party paper trail behind the income line.
None of these things is illegitimate by itself. Some people really do give a quarter of their income to charity, and the deduction is theirs to take. The difference between an uncomfortable audit and a short one is documentation: receipts, logs, and statements that answer the question the computer raised.
If the letter comes
First, confirm it is real. The IRS initiates audits by mail, not by phone call, text, or email demanding immediate payment; those are scams. Second, read what kind of exam it is. Most IRS examinations are correspondence audits conducted entirely by mail, usually about one or two specific items, and answered by sending copies of records. Office and field audits, the in-person kind, are reserved for more complex returns.
Scope is limited by the calendar, too. The IRS says it generally audits returns filed within the last three years, adding earlier years only when it finds a substantial error, and even then it usually goes back no more than six years. That timeline is also your record-keeping guide: keep the documents behind each return at least three years, and longer for property, investments, and anything unusual.
Respond by the deadline in the letter, send copies rather than originals, and answer only what is asked. You have the right to representation, and if you disagree with the outcome, the notice explains your appeal options.
Habits that keep you off the pile
The unglamorous summary: report every dollar that generates a form, keep receipts for the deductions you claim, use exact figures instead of round guesses, and think twice about positions wildly out of line with your income. E-filing helps by catching arithmetic errors that used to trigger correspondence all by themselves.
Audits will never be zero, because part of the system is random by design. But the process is not a lottery run against ordinary filers. It is mostly a comparison engine looking for returns that do not resemble their neighbors, plus a matching engine looking for income that never got reported. Give neither engine anything to find, keep your paperwork for three years, and the audit pile will almost certainly remain something you read about rather than something you live through.
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