Vehicle Deductions and Mileage Log Requirements
The IRS requires contemporaneous mileage logs documenting business vehicle usage. Standard mileage rate of 67 cents per mile (2026) requires proof of business miles driven. A business owner without mileage logs cannot claim vehicle deductions, even if the vehicle is genuinely used for business. Proper documentation supports deductions and protects against audit disallowance.
Mileage Log Content Requirements
A valid mileage log includes: date of travel, business destination, business purpose, miles driven, and odometer readings. Paper logs are acceptable; digital mileage apps (MileIQ, Everlance, TripLog) automate tracking. The IRS expects reasonable completeness; missing occasional trips may be acceptable, but systematic gaps indicate inadequate documentation.
Contemporaneous Documentation
Logs must be maintained contemporaneously (created during the period of use, not reconstructed from memory later). End-of-year reconstructions may not satisfy IRS requirements, particularly if the business owner cannot credibly recreate months of detailed mileage data. Maintain daily or weekly logs rather than annual reconstructions.
Standard Mileage Rate Calculation
Multiply business miles by 67 cents to calculate deduction. A business owner driving 25,000 business miles deducts $16,750 (25,000 miles X $0.67). This deduction includes all vehicle operating costs (fuel, maintenance, insurance, depreciation) on a per-mile basis.
Commuting and Non-Deductible Miles
Commuting from home to a regular office is personal (non-deductible). Business travel from the office to client sites is deductible. A business owner driving home to office (15 miles, non-deductible) then office to client (30 miles, deductible) can deduct only the 30 miles. Distinguish clearly between personal commuting and business travel.
Actual Expense Method Alternative
Taxpayers using actual expense method track fuel, maintenance, repairs, insurance, and depreciation. Actual expenses often exceed standard mileage rate for vehicles with high operating costs. Compare both methods annually; higher-deduction method should be used (though switching back to standard mileage is restricted).
Digital Apps and Automated Tracking
Mileage tracking apps automate log maintenance. Apps like MileIQ track miles automatically (GPS-based), allowing business purpose annotations. Digital logs satisfy IRS contemporaneous documentation requirements and are more difficult to challenge than manual logs.
Multiple Vehicles and Allocation
Business owners with multiple vehicles should track each vehicle's business usage separately. If two vehicles are used partially for business, calculate the business-use percentage for each. Some vehicles may be 100% business; others may be 50% business, 50% personal.
Business Use Percentage and Non-Business Allocation
Personal use miles cannot be deducted. A vehicle with 20,000 business miles and 10,000 personal miles is 67% business use. Under standard mileage rate, deduct 67% of annual vehicle costs (67% X vehicle's total costs). Under actual expense method, deduct only business-use percentage of depreciation, insurance, fuel, etc.
Audit Risk and Documentation
Vehicle deductions are commonly audited. Strong, contemporaneous mileage logs significantly reduce audit risk and provide defense if challenged. Weak or missing documentation often results in complete deduction disallowance. Invest in mileage tracking discipline as audit insurance.
Year-End Reconciliation
At year-end, reconcile total miles in mileage log with odometer readings. Confirm business-use percentage. Calculate total deduction and confirm it matches tax return claims. Discrepancies suggest documentation issues that should be corrected before filing.