Guides · Audit triggers
What triggers an IRS audit — and how to reduce the chance
How common audits are
For tax year 2024 (the latest full data), the IRS audited about 0.4% of individual returns overall — roughly 1 in 250. The rate varies sharply by income:
| AGI | Audit rate |
|---|---|
| Under $25,000 | ~0.3% |
| $25,000-$100,000 | ~0.2% |
| $100,000-$1M | ~0.4% |
| $1M-$5M | ~1.5% |
| $5M-$10M | ~3.5% |
| Over $10M | ~10%+ |
| EITC claimants | ~0.8% |
Most W-2 employees who take the standard deduction will never be audited. Self-employed people, investors with complex returns, and high-net-worth filers face higher rates.
How the IRS selects returns
Three selection systems:
1. Discriminant Inventory Function (DIF) score
Every individual return receives a DIF score — a numeric ranking that compares the return against norms for similar returns (same income range, same filing status, same industry code). Returns with scores above a threshold are flagged for review. The DIF score is proprietary; the IRS does not publish the exact formula, but they have released general categories of high-DIF features over the years.
2. Information matching
Forms 1099 (issued by employers, brokers, banks, payers) are filed with the IRS. If the income on your 1040 doesn't match what the 1099s say, the IRS notices. Common mismatches:
- Forgetting to include a 1099-INT, 1099-DIV, or 1099-B.
- Forgetting K-1 income from a partnership or S-corp.
- Mismatched W-2 amounts (employer reports $X, you report $Y).
- Reporting $X on 1099-INT and $Y on Schedule B (interest income).
3. National Research Program (NRP)
The NRP is the IRS's statistical sample of returns — used to update the DIF formula. NRP audits are random within stratified income brackets. A small number of returns are selected each year purely for research purposes; the resulting data updates the DIF scoring weights.
Top audit triggers
The most common DIF-score-increasing features on individual returns:
1. Income vs prior year
A 50%+ jump in income or a 50%+ drop in income relative to the prior year is a red flag. The IRS asks: did this person change jobs, take a large distribution, or omit income?
2. Round-number deductions
Returns with very round dollar amounts ($5,000, $10,000) for charitable contributions or business expenses tend to score higher than returns with messy specific amounts ($4,847, $10,243). Real deductions are rarely round.
3. Excessive business deductions relative to income
A Schedule C with expenses over 70% of gross receipts is automatically flagged for review. Most businesses operate with expenses in the 30-60% range; expenses higher than 70% suggest hobby-loss treatment or aggressive categorization.
4. Large charitable deductions relative to income
Charitable contributions exceeding 30% of AGI are scrutinized (though 60% is the AGI ceiling for cash gifts to qualified charities, anything over 30% triggers verification of the recipient's 501(c)(3) status).
5. Home office deduction
The home office deduction is a perennial audit flag. The simplified method ($5/sq ft, max 300 sq ft = $1,500) is generally accepted; the regular method (actual expenses) requires Form 8829 and is reviewed more closely.
6. Vehicle expenses
Business-use vehicle deductions over $15,000/year are commonly flagged. A mileage log is required to substantiate business use; without one, the deduction is disallowed.
7. Net operating losses (NOLs)
NOLs — particularly large ones in years when the economy is weak — are audited frequently. The Tax Cuts and Jobs Act changed NOL treatment (limited to 80% of taxable income post-2017); the IRS verifies the NOL calculation and carry forward.
8. Foreign accounts and foreign income
Returns with foreign income, foreign accounts, or foreign trust involvement are matched against FBAR and Form 8938 filings. Mismatch triggers automatic audit.
9. Cryptocurrency transactions
Crypto brokers (since 2025) issue Form 1099-DA. The IRS matches 1099-DA against the return. Mismatch or omission triggers audit; gains or losses reported inconsistently with the broker's records trigger audit.
10. Cash-intensive businesses
Restaurants, salons, taxis, valets, and other cash-heavy businesses are statistically audited more often. The IRS uses industry-specific norms and Form 8300 (cash payments over $10,000) matching.
High-risk income categories
Returns with these income types face elevated audit risk:
Self-employment income (Schedule C)
Self-employed filers are 3-5x more likely to be audited than W-2 employees, because of the absence of withholding and the larger deduction surface. Schedule C is the most audited form in the US.
Rental real estate (Schedule E)
Rental losses that exceed $25,000 and other deduction-heavy rental returns are audited more often, especially when claimed by high-income taxpayers. The passive activity loss rules (§469) limit the deductible rental loss against non-passive income; the IRS verifies the limitation calculations.
Investment income and capital gains
Returns with large capital gains, large dividend income, or complex investment transactions are matched against 1099-B and 1099-DIV filings. Wash-sale violations, basis mismatches, and missing cost basis are common triggers.
K-1 income (partnerships, S-corps, trusts)
K-1 income is matched against the entity's filing. Mismatch triggers audit of both the entity and the recipient. K-1s arriving late (after the original filing deadline) are a common source of adjustment.
Schedule C red flags
The most audited form. The IRS's industry norms for Schedule C are detailed — expense ratios by line item, per industry. Returns that deviate significantly from these norms are flagged.
Common Schedule C red flags:
- Round-number deductions.
- Vehicle expenses over $15,000 without a mileage log.
- Home office deductions without proper Form 8829.
- Meals and entertainment (50% deductible) over $5,000.
- Office expenses exceeding industry norms.
- Losses for 3+ consecutive years (hobby-loss rules apply).
- Cost of goods sold exceeding gross receipts.
- Inventory accounting discrepancies.
Net income under $50,000 with deductions under $50,000: audited rate ~0.3%. Net income over $1M: audited rate ~1.5%.
Random and correspondence audits
Random audits
A small number of returns are audited purely at random — the DIF score doesn't matter. These are usually NRP-related and are most common at low incomes (the IRS uses NRP to update formulas for low-income brackets, which are otherwise under-audited).
Correspondence audits
Most individual audits are correspondence audits, conducted by mail. The IRS sends a letter asking for documentation of specific items: charitable contribution receipts, mileage logs, dependent-care expenses, etc. The taxpayer responds by mail within 30 days. Resolved audits conclude with either no change, an agreed adjustment, or (rarely) escalation to a field audit.
Field audits
Field audits are in-person, typically at the taxpayer's home or business, and more common for businesses and high-net-worth filers. The IRS sends an agent who reviews records on site. Field audits can last months.
How to reduce audit risk
- Report all income. 1099s, W-2s, K-1s. The IRS already has this data; omitting it is the easiest way to be flagged.
- Keep documentation. Receipts for charitable contributions, logs for mileage, statements for rental expenses. The audit is won or lost on documentation, not on the return itself.
- Use specific numbers. If your deductions are real, they're rarely round. $4,847 looks more credible than $5,000.
- Stay within industry norms. If your restaurant reports a 90% expense ratio and the industry norm is 65-75%, you're flagged. Use Form 1099-NAICS data to check your ratios.
- Use professional preparation. Returns prepared by a CPA or EA are not necessarily less likely to be audited, but they are less likely to contain triggering errors. A prepared return also documents that you exercised reasonable care.
- Avoid unusual positions. If you're claiming a deduction or credit that 99% of similar filers don't claim, expect questions.
- Reconcile Forms W-2 and 1099 carefully. Information matching is the most common audit trigger. Many audits are correspondence audits triggered solely by a W-2/1099 mismatch.
- Don't overdo the home office. The simplified method ($1,500 max) is audit-resistant; the regular method invites review.
If you are audited
- Read the IRS notice carefully. It will specify what the IRS is asking for, what years are being audited, and the response deadline (usually 30 days).
- Don't panic. Most correspondence audits are narrow and resolved with documentation.
- Gather the requested documents. Do not send what wasn't asked for — providing extra documents invites additional questions.
- Consider professional representation. CPAs, EAs, and tax attorneys can respond on your behalf with a Form 2848 (Power of Attorney).
- Appeal if you disagree. The IRS has an internal appeals process (IRS Office of Appeals) that resolves most disputes without going to tax court.
The TaxToNet calculator is a baseline; an audit considers your actual return with credits, deductions, and income documentation. Use the calculator to understand the math; use a qualified tax professional if you're facing an audit.