The word audit strikes fear into most business owners — but it does not have to. Audits are manageable when your bookkeeping is clean and your records are complete. Most business audits result in no change or small adjustments when the taxpayer has good records. Here is how to be audit-ready at all times.
What Triggers a Business Audit
The IRS uses statistical models to identify returns that look unusual compared to similar businesses. Common audit triggers include: high deductions relative to income (especially Schedule C losses), cash-intensive businesses (restaurants, contractors, retail), home office deductions, large vehicle deductions, claiming 100% business use of a vehicle, large charitable contributions, significant changes in income year over year, and mathematical errors on the return. Minnesota Department of Revenue audits often focus on sales tax compliance — especially businesses that should be collecting sales tax but are not.
The Records You Must Have
For a business audit, you need to substantiate every item on your tax return. The essential records are: bank statements for all business accounts (IRS can request 3 years, sometimes 6), credit card statements, receipts for all business expenses (especially those over $75), mileage logs if you deduct vehicle expenses, home office documentation (square footage, utility bills, mortgage/rent statements), payroll records and tax deposits, business contracts and invoices, records of business meals (who, what business purpose, amount), and prior year tax returns.
The 7-Year Retention Rule
The IRS generally has 3 years from your filing date to audit you. But they have 6 years if you underreported income by more than 25%, and there is no limit if they suspect fraud. For safety, keep all business records for at least 7 years. Records related to property (for depreciation) should be kept for 7 years after you sell the property. Store digital copies in the cloud — physical records can be destroyed in fires or floods.
Mileage Log Requirements
Vehicle deductions are heavily audited because they are commonly abused. The IRS requires a contemporaneous mileage log (recorded at the time of the trip, not reconstructed later). Your log must show: date of each business trip, starting and ending odometer reading or total miles, destination, and business purpose. Apps like MileIQ or TripLog make this simple. The standard mileage rate for 2025 is 70 cents per mile.
Home Office Documentation
To deduct a home office, you must use a portion of your home regularly and exclusively for business — a dedicated room, not a corner of your bedroom. Measure the square footage of your office and divide by total home square footage. This percentage applies to rent/mortgage interest, utilities, insurance, and repairs. Take photos of your home office annually. The simplified method ($5/square foot, max 300 sq ft) requires less documentation.
How Good Bookkeeping Is Your Best Defense
When audited, you will be asked to provide documentation for specific line items on your return. If your books are well-organized with every expense categorized and supported by a receipt or invoice, your responses are fast and confident. If your books are a mess, you spend weeks reconstructing transactions — and what you cannot document gets disallowed. Businesses with clean books, reconciled accounts, and organized records almost always fare better in audits than those without.
Minnesota Sales Tax Audits
The MN Department of Revenue conducts sales tax audits separately from income tax audits. They will review your sales records, exemption certificates from tax-exempt customers, and whether you correctly identified taxable vs. exempt sales. Common findings: not charging sales tax on taxable services, missing or invalid exemption certificates, and errors in local tax rates. Keep all exemption certificates for at least 3.5 years after the filing date of the return they relate to.