What actually triggers an IRS audit (and what to do if a letter arrives)

Audit anxiety is wildly out of proportion to audit reality: the IRS audits well under 1% of individual returns, and most 'audits' are letters asking about one line item — not agents in your living room. The system is mostly a document-matching computer. Understand what the computer flags, and both avoiding trouble and responding to it become straightforward.

What actually gets returns flagged

• Mismatched documents — the #1 trigger by far. Every W-2 and 1099 is matched to your return by computer; a missing form generates an automatic notice, no human needed.
• Very high income: audit rates climb steeply above $500k and especially $1M+, simply because that's where the money is.
• EITC claims: heavily audited (via correspondence) because the rules about qualifying children are genuinely confusing — this is why lower-income filers get audited more than the middle class.
• Self-employment with suspicious patterns: round numbers everywhere, losses year after year (hobby-loss territory), 100% business use of a vehicle, or deductions far above the norm for your income and industry.
• Large cash transactions and cash-heavy businesses.
• Big charitable deductions relative to income, and noncash donations over $5,000 without an appraisal.
• Claiming things that don't exist: fuel tax credits for commuters, invented household employees — the 'too good to be true' credits promoted on social media.

The letters, ranked by seriousness

1. Math error / adjustment notices (e.g., CP12): the IRS fixed an arithmetic issue and changed your refund. Read, verify, usually done.
2. CP2000 — the mismatch letter: 'our records show income you didn't report, here's the proposed extra tax.' Not an audit; a proposal you can accept or contest.
3. Correspondence audit: a letter asking you to mail documentation for specific items (EITC, charitable deductions). The most common true audit.
4. Office or field audit: an in-person examination. Rare, generally reserved for businesses and high-income complexity — and the point where hiring representation stops being optional.

If a letter arrives: the playbook

1. Open it immediately. Every bad IRS outcome is downstream of ignored mail — deadlines (usually 30 days) are what convert proposals into assessed debts.
2. Verify it's real: the IRS initiates contact by postal mail, not by phone call, email, or text demanding gift cards. Check the notice number on irs.gov.
3. Read what's actually asked. Most letters concern ONE item and one tax year. Answer that item only — volunteering extra information can expand the inquiry.
4. Agree? Sign and pay (installment plans can start the same day). Disagree? Respond in writing by the deadline with copies (never originals) of your documentation.
5. Keep records of everything: send responses by certified mail, keep copies, note the dates.
6. Get help when stakes rise: a CPA or enrolled agent can represent you entirely (you never speak to the IRS yourself). For hardship situations, the Taxpayer Advocate Service and Low Income Taxpayer Clinics are free.

Audit-proofing in practice

• Report every form you receive, even when the taxable amount is zero — attach the explanation rather than omit the form.
• Keep records 3 years minimum (the standard audit window), 7 for anything involving losses or bad debts; the window is unlimited for unfiled or fraudulent returns.
• Document deductions in real time: mileage logs, receipts photographed into a folder, appraisals for big donations.
• E-file — paper returns have far higher error and processing-problem rates.

Your actual odds

Those odds also come with a statute of limitations: the IRS generally has three years from filing to examine a return, six if income was underreported by more than 25%, and forever only for fraud or unfiled years. In practice most notices arrive 12-18 months after filing — which is why the CP2000 about your 2024 return shows up in late 2026, long after you've stopped thinking about that year. It isn't an escalation; it's just the speed of the matching computers. Keep each year's records until its window closes and every letter becomes an exercise in photocopying rather than archaeology.

The bottom line

Audits are rare, mostly automated, and mostly about mismatches and missing proof — not about honest returns with real deductions. Report everything the IRS already has a copy of, keep documentation for what you claim, open every letter the day it arrives, and treat proposed amounts as first offers subject to your paperwork. The taxpayers who get hurt are almost never the ones who engaged; they're the ones who hoped it would go away.

It's also worth right-sizing the fear financially. The worst realistic outcome of a correspondence audit for an honest filer is repaying tax on an item you couldn't document, plus 20% and interest — unpleasant, survivable, and usually in the hundreds or low thousands of dollars. People routinely forgo legitimate five-figure deductions over a risk with a three-figure expected cost. Claim what's yours, keep the receipts, and let the math of rare audits and modest penalties work in your favor the way it actually runs.