What Triggers an IRS Audit?

Most IRS audits are statistical, not personal. The IRS uses computer scoring models — primarily the Discriminant Inventory Function (DIF) score — to compare your return against other returns with similar income and deductions. Returns that score outside the normal range get flagged for human review. A reviewer then decides whether the anomaly justifies an audit.

A smaller share of audits come from automatic triggers: missing third-party reporting (a 1099 filed against your SSN that you did not include), referrals from another taxpayer's audit, related-party transactions, and a few specific high-risk situations.

The most common audit triggers

A handful of patterns account for most flagged returns:

• Income that does not match third-party reporting. The IRS receives copies of every W-2, 1099, 1098, K-1, and similar form. If you under-report income relative to what the IRS already has, expect a CP2000 notice (which is technically not a full audit but functions like one) or a true audit. This is the single most common trigger.
• Schedule C with high deductions relative to revenue. Self-employed taxpayers with home offices, vehicle expenses, and meals deductions get scored more carefully than W-2 employees. The DIF model compares your deduction-to-revenue ratios against industry norms. Outliers get flagged.
• Cash-intensive businesses. Restaurants, salons, retail, contractors paid in cash, and similar businesses are audited at higher rates because the income is harder to verify. The IRS uses bank deposit analysis, lifestyle audits, and indirect methods to estimate true income.
• Large charitable deductions relative to income. A taxpayer claiming $30,000 of cash and non-cash charitable gifts on $80,000 of income will score higher than the same gifts on $400,000 of income. The IRS expects supporting documentation: appraisals for non-cash donations over $5,000, contemporaneous written acknowledgments for any single gift over $250.
• Round numbers and estimates. Returns full of round-number deductions ($10,000 vehicle, $5,000 supplies, $2,500 meals) signal estimation rather than recordkeeping. Real expenses are rarely round.
• Unreported foreign accounts. Failure to file FBAR (FinCEN 114) or Form 8938 when required carries significant penalties and is a common audit driver for taxpayers with overseas ties.
• Crypto activity not reported on Form 8949. Exchanges send 1099-B and 1099-DA forms to the IRS. A return without crypto activity, when the IRS shows you have it, is now a routine flag.

Audit rates by income bracket

Overall audit rates have fallen substantially over the last decade. The IRS Data Book shows the most recent overall audit rate at less than 0.5% of individual returns. Audit rates rise at the very top (incomes over $10 million) and at the very bottom (taxpayers claiming the Earned Income Tax Credit, which the IRS audits at higher-than-average rates because of error patterns).

For taxpayers in the middle (say, $50,000-$500,000 in income), audit rates are very low — often below 0.3%. Most middle-income audits are correspondence audits (mail-based, single-issue) rather than office or field audits.

Three audit types

• Correspondence audit. Most common. The IRS sends a letter asking for documentation on one or two specific items. Typical issues: charitable deductions, business expenses, dependents, EITC eligibility. Resolved by mail.
• Office audit. You go to a local IRS office with documentation. Used for moderately complex returns or multiple issues.
• Field audit. An IRS Revenue Agent comes to your home, business, or representative's office. Reserved for businesses, high-income individuals, or complex returns. Field audits are the most thorough and the most consequential.

What to do if you are selected

If your return is selected, how you respond shapes the outcome:

• Read the notice carefully. Audit notices specify what is being examined and what documentation is required. Do not volunteer information about anything not on the notice — the scope of the audit can expand if you do.
• Pull together the documentation requested: receipts, bank statements, mileage logs, contemporaneous calendars, written acknowledgments. Reconstruct what you can if records are missing.
• Get representation if the audit is in-person, if the dollar amounts are significant, or if any item involves potential fraud or willfulness. Power of Attorney (Form 2848) lets a CPA, EA, or tax attorney handle the audit on your behalf — you do not have to attend the meetings.
• Appeal an assessment you disagree with. If you have already lost the audit, a tax appeal is your next step. The IRS Office of Appeals settles a substantial share of cases without litigation.

Getting ahead of an audit

The single biggest protection against a bad audit outcome is documentation that exists before the audit begins. Contemporaneous records — kept as the year goes — are far more credible than reconstructed records. Mileage logs, receipts attached to bank statements, calendar entries supporting business meals, written acknowledgments for charitable gifts.

If your business is in a high-audit category (Schedule C, cash-intensive, or large deductions), professional representation with audit-defense as a goal pays for itself many times over. Most audit losses come from missing documentation, not from bad positions.