Most IRS audits aren't random. They're triggered by specific red flags — patterns in your tax return that the IRS's automated systems flag for review. Here are the seven most common bookkeeping mistakes that increase your audit risk.

1. Mixing Personal and Business Expenses

Running personal expenses through your business account — or vice versa — is the single most common bookkeeping error. It creates a messy paper trail, inflates deductions, and raises immediate red flags if audited. The fix: a dedicated business bank account and credit card, used exclusively for business.

2. Claiming 100% Business Use of a Vehicle

The IRS knows that very few people use a vehicle 100% for business. A mileage log is required to substantiate vehicle deductions. Without one, the deduction is disallowable. With a mileage app like MileIQ, this takes 30 seconds a day.

3. Large, Round-Number Deductions

Claiming exactly $10,000 for meals or $5,000 for office supplies — round numbers signal estimation rather than actual tracking. Every deduction should be supported by receipts and a clear business purpose.

4. Home Office Deductions Without Proper Documentation

The home office deduction is legitimate but heavily scrutinized. The space must be used regularly and exclusively for business. Document square footage, calculate the correct percentage, and keep utility bills.

5. Inconsistent Revenue Reporting

The IRS receives 1099s, W-2s, and third-party payment processor reports (PayPal, Stripe). If your reported income doesn't match what's been reported to the IRS by third parties, you'll get a CP2000 notice at minimum.

6. Excessive Meals & Entertainment

Meals are 50% deductible (entertainment is no longer deductible at all post-TCJA). A meals expense that equals 20–30% of your revenue is a red flag. Document each meal: who attended, business purpose, and keep the receipt.

7. Not Reconciling Bank Statements Monthly

Unreconciled books mean errors compound over time. By year-end, you may be missing income, double-counting expenses, or carrying ghost transactions. Monthly reconciliation catches issues immediately when they're easy to fix.

The best audit defense is clean, well-documented books. If you're audited with Advisory Monks Consulting's bookkeeping behind you, every transaction is categorized, reconciled, and supportable.