What Triggers an IRS Audit of a Small Business
How returns get selected, the patterns that draw attention on business returns, what each type of audit looks like, and how long the IRS has to ask.
Reviewed by the Fairlight Accounting cross-border tax team — U.S. & Canadian Tax Desks
The IRS picks returns for audit through computer scoring against norms for similar returns, matching income against third-party forms such as 1099s, random samples, and examinations of related taxpayers. Red flags are patterns, not violations: large round numbers, deductions out of proportion to income, repeated losses, and missing income reported elsewhere. Good records turn most audits into document exercises.
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How are returns selected?
- Computer scoring. The Discriminant Inventory Function (DIF) system scores each individual return and some corporate returns against norms developed from random-sample audits. A high score means an audit is likely to change the tax. Some returns are also picked purely at random.
- Document matching. The IRS matches 1099-NEC, 1099-K, 1099-MISC, W-2, and other forms against your return. A mismatch usually generates a notice, such as a CP2000, rather than a full audit.
- Related examinations. An audit of a business partner, customer, or investor can lead to yours.
- Market segments and outside information. A return may be picked to study how similar taxpayers handle an issue, or because of information from public records or other sources.
What patterns draw attention?
| Pattern | Why it stands out |
|---|---|
| Income lower than the 1099s and 1099-Ks reported | Automatic mismatch |
| Losses year after year on Schedule C | Suggests a hobby or personal expenses |
| Vehicle claimed at 100 percent business use | Hard to support; mileage records are required |
| Large meal and travel deductions relative to income | Easily mixed with personal spending |
| Round numbers across many lines | Suggests estimates rather than records |
| S corporation owner with distributions and little or no salary | Reasonable compensation issue |
| Cash-heavy business with low reported margins | Margins far below similar businesses stand out against return norms |
| Large charitable deductions relative to income | Valuation and documentation questions |
| Workers paid as contractors who look like employees | Employment tax exposure |
None of these is improper when it is accurate. The risk is a deduction you cannot prove.
What do the different audits look like?
- Correspondence audit. A letter asks for documents on one or two items. This is the most common type: 81 percent of the audits the IRS closed in fiscal year 2025 were by correspondence, nearly all of them on individual returns.
- Office audit. You or your representative meet an examiner at an IRS office.
- Field audit. An examiner visits the business, reviews the books, and may interview the owner. Audits of corporation, S corporation, and partnership returns are overwhelmingly field audits.
You may be represented by an authorized professional under Form 2848 and generally need not attend meetings yourself unless the IRS issues a summons.
How far back can the IRS go?
Generally three years from the later of the filing date or due date. The period extends to six years if you omitted more than 25 percent of gross income, and there is no limit for fraud or for a return never filed. Keep records at least that long, and longer for assets you still own.
How do you respond?
Read the letter carefully, note the deadline, and answer only the items asked. Send organized copies — never originals — with a short cover explanation. If you disagree with proposed changes, you can request a conference with a manager or appeal within the deadline in the letter.
Frequently asked questions
Does filing an extension increase audit risk?
Nothing the IRS publishes says so. Its published selection methods are computer scoring, document matching, random samples, and related examinations — not extensions, which are routine.
Does a home office deduction trigger an audit?
The IRS does not name it as a selection factor. It must meet the regular-and-exclusive-use test, and it should be supported with a floor plan and expense records.
Is an IRS phone call or email about an audit real?
The IRS starts audits by mail. Unsolicited calls, texts, or emails claiming to be an audit are almost always scams.
Can an audit result in a refund?
Yes. Examiners adjust items in both directions — in fiscal year 2025, 16,158 IRS examinations resulted in refunds to taxpayers.
Official sources
The IRS explains: “Random selection and computer screening - sometimes returns are selected based solely on a statistical formula. We compare your tax return against "norms" for similar returns.” — Internal Revenue Service, IRS audits, https://www.irs.gov/businesses/small-businesses-self-employed/irs-audits
The IRS explains: “Keep records for 6 years if you do not report income that you should report, and it is more than 25% of the gross income shown on your return.” — Internal Revenue Service, How long should I keep records?, https://www.irs.gov/businesses/small-businesses-self-employed/how-long-should-i-keep-records
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