Schedule C Audit Triggers: What the IRS Looks For in Small Business Returns
The overall audit rate for individual returns is low: the IRS has examined about 0.36% of individual returns filed for tax years 2015 through 2023 (2025 IRS Data Book). The Data Book doesn’t publish a separate audit rate for Schedule C filers. The IRS uses a scoring system (the DIF score, Discriminant Function) that compares each return to “norms” for similar returns, built from audits of a random sample of returns. Generally, the higher the score, the greater the audit potential. The formulas themselves are confidential.
The IRS doesn’t publish what raises a Schedule C score (its DIF formulas are confidential), so no list is official. Patterns worth a second look before you file: (1) Repeated losses (a business that doesn’t show a profit in at least 3 of 5 years can’t use the IRC 183 presumption that it’s run for profit, which opens the hobby question; missing the presumption doesn’t create a presumption of a hobby). (2) Deductions out of line with income (the IRS compares each return to “norms” for similar returns). (3) Cash-intensive businesses (IRS tax gap research doesn’t single out cash, but for tax years 2014 to 2016 it put the net misreporting rate at 55% for income with little or no third-party reporting, such as sole proprietor income). (4) Round numbers (deductions in round thousands, like $5,000 for meals and $10,000 for travel, look estimated, and the IRS says you can’t deduct amounts you approximate or estimate). (5) Large vehicle deductions (any business-use claim, 100% included, should be backed by a mileage log showing each business trip and your total miles for the year). (6) Home office deduction (under either method, the space generally must be used regularly and exclusively for business). (7) Mismatched 1099 income (the IRS matches the 1099s it receives to your return through its Automated Underreporter Program). (8) Large meal deductions (business meals are generally 50% deductible, and entertainment isn’t deductible at all). None of these are reasons to avoid legitimate deductions. The strategy is to claim every deduction the business is entitled to, document each one thoroughly, and be prepared to substantiate the deduction if questioned.
What documentation protects against an audit?
IRC 274(d) requires adequate records (or sufficient evidence backing up your own statement) for travel, including meals while away from home, gifts, and vehicles and other listed property. Entertainment isn’t deductible at all. For current guidance, see IRS Schedule C instructions. For other expenses, the general substantiation rules apply: receipts, invoices, bank statements, and a clear business purpose.
Vehicle deduction: A contemporaneous mileage log (date, destination, business purpose, miles) is the gold standard. Apps like MileIQ automate this. Without a log, the IRS can disallow the entire vehicle deduction.
Meals: The receipt plus a note identifying who attended, the business relationship, and the business purpose. “Lunch with Dana Lee (client), discussed Q4 campaign” covers who attended, the relationship and the purpose. “Lunch” alone does not.
Home office: For the simplified method, no documentation of home expenses is needed (just the square footage). For the actual method: receipts for rent/mortgage interest, utilities, insurance, repairs, and the square footage calculation.
Supplies and equipment: Receipts or credit card statements. The de minimis safe harbor (items up to $2,500 per invoice or item, for businesses without an applicable financial statement) is elected by attaching a statement to your timely filed return for each year you use it.
What if the IRS audits?
Most individual return audits are done by mail: 393,767 of the 441,578 individual return audits the IRS closed in fiscal 2025 were correspondence audits (IRS Data Book). The IRS sends a letter requesting documentation for specific items. The business owner responds by mail with copies of receipts, logs, and records. If the documentation supports the deduction, the audit is closed with no change.
An in-person audit (less common) involves an IRS agent reviewing records at the taxpayer’s office or the agent’s office. The agent reviews bank statements, receipts, and records for the items under examination.
The statute of limitations for IRS audits is generally 3 years from the filing date. If you leave out income that’s more than 25% of the gross income shown on the return, the statute extends to 6 years. There’s no statute of limitations for fraud.
What records do I need to keep to support my business deductions?
For travel (including meals while away from home), gifts and vehicles, IRC 274(d) requires records that show the amount, the time and place, the business purpose and, where it applies, the business relationship. For those expenses, you need a receipt or similar documentary evidence for lodging and for any other expense of $75 or more; under $75 (other than lodging), a written record with these details is enough. For other expenses, keep records that support the amount and the business purpose, such as invoices and receipts. A canceled check or card statement by itself doesn’t prove a business expense without other evidence of the business purpose, though it can back up your records. Record each expense at or near the time (a weekly log counts as timely). Entertainment isn’t deductible at all. Records kept on a computer count as adequate records.
What records do I need to keep to substantiate my tax deductions?
For travel, gifts and vehicle expenses, the IRS requires records that show the amount, date, place, and business purpose of each expense. For those expenses, you need a receipt for lodging and for anything of $75 or more; under $75, a log entry or digital note with the details is enough. Bank and credit card statements alone are not sufficient documentation because they show the amount and vendor but not the business purpose. For meals, you must record who was present and the business topic discussed, in addition to the receipt (needed at $75 or more). For vehicle expenses, keep a timely mileage log (paper or digital app) showing the date, destination, business purpose and miles for each business trip, plus your total miles for the year; odometer readings are the simplest way to get those numbers. The IRS can disallow deductions entirely if you cannot produce records during an audit, even if the expenses were legitimate.
Related guides:
Start with a Diagnostic: a CPA licensed in the US and Canada reads your file and tells you in writing what's wrong and how to fix it, three to four business days after you finish the questions. The report is $250. If you hire us for any work after that, you get the $250 back as a discount on that work. Or send us your return or your letter and get a fixed price, free.
One or two plain-English guides a week on US-Canada tax. No spam, unsubscribe anytime.
Done. The next guide will land in your inbox.
Yarik Yarosh, CPA. "Schedule C Audit Triggers: What the IRS Looks For in Small Business Returns." Blue Cloud CPA, September 5, 2026, updated October 18, 2026. https://bluecloudcpa.com/guides/small-business-audit-triggers-schedule-c
This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.